Nothing was pointing at BBGE/glext.
Only the VS project was pointing at ExternalLibs/GL. I have pointed it
at the headers under BBGE/GL instead.
I have also adjusted the includes to use the GL prefix as is standard
practise. These will still work as BBGE is in the include path. This
allows users to build against their system GL headers simply by
deleting the BBGE/GL directory.
This untangles some of the gigantic kitchen sink headers
in an attempt to split things into smaller files.
Also don't include gl.h, glext.h, windows.h,
and other such nonsense *everywhere*.
Lots of cleanups on the way too. More dead/unused code removal.
Remove incrFlag(), decrFlag() Lua functions.
