Bring back "Game mode indeterminate" error...

...for non-Windows builds, since launcher won't be displayed.
Fix HUD crashing in BFG Edition
Fix corrupt palette for BFG Edition DOOM2.WAD
Fix a couple of remaining issues for Linux build

Courtesy of @Luke-Nukem.
Don't try to fix "videodriver" in non-Windows
Merge https://github.com/bradharding/doomretro

Conflicts:
	src/Makefile
	src/hu_stuff.c
	src/sounds.c
	CodeBlocks Project
	new file:   DoomRetro.cbp