This fixes the prior logic that relies on the (*)curses library
and header existing in compiler-derived default locations
such as /usr/include, and /usr/lib. However, if the package manager
happens to not install them there, then they will not be found
and the check will fail.
Four scenarios:
1. `./configure` or `./configure --enable-debug=no` produce:
    (no mention of debugger; configure continues)
2. `./configure --enable-debug=wrong` produces:
    configure: error: --enable-debug=wrong was requested but the value "wrong" is invalid
    (terminates with exit code 1)
3. `./configure --enable-debug` produces:
    config.h:
    defines C_DEBUG 1
    With only ncurses library installed:
    configure: debugger was requested, finding curses library ...
    checking for NCURSES... yes
    configure: debugger enabled using the ncurses library
    Makefile:
    CPPFLAGS = ... -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=600 -I/usr/local/ncurses ...
    LIBS = ...  -L/usr/local/ncurses -lncurses -ltinfo ...
    With only ncursesw installed:
    configure: debugger was requested, finding curses library ...
    checking for NCURSES... no
    checking for NCURSESW... yes
    configure: debugger enabled using the ncursesw library
    Makefile:
    CPPFLAGS = ... -I/opt/ncursesw ...
    LIBS = ... -L/opt/ncursesw -lncursesw ...
    With only pdcurses isntalled:
    configure: debugger was requested, finding curses library ...
    checking for NCURSES... no
    checking for NCURSESW... no
    checking for PDCURSES... yes
    configure: debugger enabled using the pdcurses library
    Makefile:
    CPPFLAGS = ... -I/usr/local/pdcurses ...
    LIBS = ...  -L/usr/local/pdcurses -lpdcurses -ltinfo ...
    Without any curses library installed:
    configure: debugger was requested, finding curses library ...
    checking for NCURSES... no
    checking for NCURSESW... no
    checking for PDCURSES... no
    configure: error: Package requirements were not met:
    <pkg-info prints info about missing package>
    (terminates with exit code 1)
4. `./configure --enable-debug=heavy` produces same as above, but:
    config.h:
    defines C_DEBUG 1
    defines C_HEAVY_DEBUG 1
    The configure message mentions heavy, for example:
    configure: debugger was requested, finding curses library ...
    checking for NCURSES... yes
    configure: debugger with heavy debugging enabled using the ncurses library
		
	
			
		
			
				
	
	
		
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| DOSBox uses the following libraries:
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| 
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| SDL
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|     The Simple DirectMedia Library available at https://www.libsdl.org/
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|     The dll distributed with the windows version of DOSBox is slightly
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|     modified. You can find the changes in the sourcepackage of DOSBox
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|     (src/platform/sdl-win32.diff). If you want the patched sourcetree
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|     send us an email. (see README)
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|     Note that only version 1.2 and its subversions (1.2.8, 1.2.13 etc.)
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|     are currently supported.
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|     License: LGPLv2+
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| 
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| Opusfile, by Xiph
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|     For compressed audio tracks (.opus) used with CDROM images.
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|     Sources are available at https://opus-codec.org, however it is
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|     also conveniently packages by all popular package managers for
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|     Windows (MSYS2, MinGW, and Chocolatey), Linux (apt, dnf, zypper,
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|     pacman), and OS X (Homebrew and MacPorts).  Opus is today's
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|     leading compression format and has replaced Vorbis as Ogg's
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|     recommended lossy format. Is widely used in the largest audio and
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|     video distribution platforms such as YouTube.
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|     License: three-clause BSD
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| 
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| Curses (optional)
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|     If you want to enable the debugger you need a curses library.
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|     On Linux, install ncurses-devel via your distro package manager.
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|     On macOS, install ncurses via brew or macports.
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|     On Windows, install pdcurses at https://pdcurses.org/, or ncurses
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|     via package-manager such as pacman within an MSYS2 environment.
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|     Licenses:
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|       ncurses - MIT License
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|       pdcurses - Public Domain
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| 
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| Libpng (optional)
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|     Needed for the screenshots.
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|     For win32 get libpng from http://gnuwin32.sourceforge.net/packages.html
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|     See http://www.libpng.org/pub/png/ for more details.
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|     License: zlib/libpng
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| 
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| Zlib (optional)
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|     Needed by libpng.
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|     For win32 get libz (rename to zlib) from http://gnuwin32.sourceforge.net/packages.html
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|     See https://www.zlib.net/ for more details.
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|     License: zlib
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| 
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| SDL_Net (optional)
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|     For modem/ipx support.
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|     Get it from https://www.libsdl.org/projects/SDL_net/release-1.2.html
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|     License: LGPLv2+
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| 
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| alsa-lib (optional)
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|     For ALSA audio support under linux. Get it from https://www.alsa-project.org/
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|     Licensed under LGPL
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| 
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| If you want compile from developer sources (SVN) under a unix system, you will need:
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|  - Subversion to checkout the sources, or gzip and tar to unpack them from archive
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|  - GCC (>=4.8.1) or Clang (>=3.3)
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|  - automake (>=1.6)
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|  - autoconf (>=2.50)
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|  - autoconf-archive (>=2009.x)
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|  - make (>= 3.8)
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|  - pkg-config (>= 0.25)
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| 
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| For building on unix systems.
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| If you are building from developer sources run ./autogen.sh first before doing
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| the following:
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| 
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|     $ ./configure
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|     $ make
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| 
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| You can also run "./configure --help" for extra features to enable/disable.
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| Some of them are:
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| 
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| --enable-debug
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|         enables the internal debugger. --enable-debug=heavy enables even more
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|         debug options. To use the debugger, DOSBox should be run from an xterm
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|         and when the sdl-window is active press alt-pause to enter the
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|         debugger.
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| 
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| --disable-core-inline
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|         disables some memory increasing inlines. This speeds up compilation,
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|         but may result in a slower dosbox.
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| 
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| --disable-fpu
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|         disables the emulated fpu. Although the fpu emulation code isn't
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|         finished and isn't entirely accurate, it's advised to leave it on.
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| 
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| --disable-fpu-x86
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| --disable-fpu-x64
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|         disables the assembly fpu core. Although relatively new, the x86/x64
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|         fpu core has more accuracy than the regular fpu core.
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| 
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| --disable-dynamic-x86
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|         disables the dynamic x86/x64 specific cpu core. Although it might be
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|         a bit unstable, it can greatly improve the speed of dosbox on x86 and
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|         x64 hosts.
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|         Please note that this option on x86/x64 will result in a different
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|         dynamic/recompiling cpu core being compiled than the default.
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|         For more information see the option --disable-dynrec
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| 
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| --disable-dynrec
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|         disables the recompiling cpu core. Currently x86/x64 and arm only.
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|         You can activate this core on x86/x64 by disabling the dynamic-x86
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|         core.
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| 
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| --disable-dynamic-core
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|         disables all dynamic cores (same effect as --disable-dynamic-x86
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|         or --disable-dynrec).
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| 
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| --disable-opengl
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|         disables OpenGL-support (output mode that can be selected in the
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|         DOSBox configuration file).
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| 
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| --disable-unaligned-memory
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|         disables unaligned memory access.
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| 
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| Check the src subdir for the binary.
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| 
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| NOTE: If capslock and numlock appear to be broken. open
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| src/ints/bios_keyboard.cpp and go to line 30 and read there how to fix it.
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