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.
Let scons link directly in the build folder.
Multiple archs can coexist next to each other.
New scons variable "X86" to cross compile x86 binaries on x86_64.
