- Changed compilation for g_doom, g_heretic, g_hexen and g_strife folders

so that all files are included by a central one instead of compiling 
  each one separately. This speeds up the compilation process by 25%
  when doing a complete rebuild in Visual C.
- Cleaned up more header dependencies.

SVN r1226 (trunk)

src/m_menu.cpp

@@ -45,6 +45,7 @@
 #include "i_system.h"
 #include "i_video.h"
 #include "v_video.h"
+#include "v_palette.h"
 #include "w_wad.h"
 #include "r_local.h"
 #include "hu_stuff.h"