Completely overhauled OpenGL/GLUT detection magic, making things more
modular. Removed support for Mesa and non-HW-accelerated support on
Windoze. Added initial support for handling missing glut.h header on
MinGW/MSYS (to be completed). Tested on Cygwin (plain, -mno-cygwin,
--without-x), MSYS/MinGW and SuSE 8.2 x86 Linux.