turns out tri->numIndexes can be quite big so _alloca16() would be
called with >1MB - and the Win32 stack only is 1MB, so that overflows.
As a workaround, use Mem_Alloc16() if we need >600KB
was reported in #265
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.
