- 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_cheat.cpp

@@ -39,7 +39,6 @@
 #include "w_wad.h"
 #include "a_keys.h"
 #include "templates.h"
-#include "p_lnspec.h"
 #include "c_console.h"
 #include "r_translate.h"
 #include "g_level.h"