Add OpenGL 4.0-4.5 core extensions.

This noticeably includes GL_ARB_get_program_binary, which was previously
thought unsupported on OS X.  Well, actually, the OS X implementation is
trivial and reports 0 binary formats (as of 10.10; this is hardcoded in
GLEngine, by the way), but at least it'll work if it's fixed someday.
Merge pull request #1185 from comex/opengl-core-extensions

Add OpenGL 4.0-4.5 core extensions.