incl. backwards compat for older savegames.
only partly useful: old savegames only work if you didn't change the
gamedata, with the CstDoom3 .gui files, loading them crashes. I don't
think that can be avoided, apparently Doom3 has no way to detect that
the GUIs have changed?
Don't include the lazy precompiled.h everywhere, only what's
required for the compilation unit.
platform.h needs to be included instead to provide all essential
defines and types.
All includes use the relative path to the neo or the game
specific root.
Move all idlib related includes from idlib/Lib.h to precompiled.h.
precompiled.h still exists for the MFC stuff in tools/.
Add some missing header guards.
