gl_common: OpenGL 3.x context support on windows
Also include GL/glext.h on windows:
Mingw's (and cygwin's) GL/gl.h has GL/glext.h's inclusion commented
out for some reason. Their glext.h is also ancient, so do yourself
a favor and replace your GL/glext.h with the one from
http://www.opengl.org/registry/api/glext.h .
A workaround is needed for NVidia's broken wglCreateContextAtrribsARB:
It'll return an error if the requested OpenGL version is previous to
3.2 *and* you request a profile... which is exactly *not* what the
wgl_create_context spec says should happen.
Handle it by removing the profile request from attribs[] and retrying
the context creation once more if the first try fails.
And after my first foray into OpenGL I already find a driver quirk.
Oh well.