- 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/thingdef/thingdef_codeptr.cpp

@@ -63,7 +63,9 @@
 #include "a_sharedglobal.h"
 #include "thingdef/thingdef.h"
 #include "v_video.h"
+#include "v_font.h"
 #include "doomstat.h"
+#include "v_palette.h"
 
 
 static FRandom pr_camissile ("CustomActorfire");