- 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/textures/flattexture.cpp

@@ -37,6 +37,7 @@
 #include "files.h"
 #include "r_data.h"
 #include "w_wad.h"
+#include "v_palette.h"
 
 //==========================================================================
 //