Changed E_Exit to warning when direct copyflag is used.
Added printscreen/scrollock/pause to the keymapper.
Ignoring printscreen and pause in keyboard (can be used to map special keys
to).
Added some binds so you can bind special keys to them (MK_scrolllock and
MK_pause).
Updated headers to support those new keys and MK_keys.
Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@1861