Fixed problems with mouse locked and switching to mapper.

Added and exit button
Changed the way the mapper behaves if you want to add a new bind to a key.
Now it clears the screen so it's more clear that you pressed the add-key.


Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@1831

include/video.h

@@ -62,5 +62,9 @@ void GFX_SwitchFullScreen(void);
 bool GFX_StartUpdate(Bit8u * & pixels,Bitu & pitch);
 void GFX_EndUpdate(void);
 
+/* Mouse related */
+void GFX_CaptureMouse(void);
+extern bool mouselocked; //true if mouse is confined to window
+
 #endif