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.

...I'm not totally familiar with this code, so I'm not sure if this is correct, although I don't see why it wouldn't be.