Fix most GLhandleARB warnings on OS X with a big comment in our code.
Remove a bad alias of glGetAttachedShaders.

On OS X, GLhandleARB is void *, which is of different size than GLuint
on 64-bit.  Because of this, the implementation of
glGetAttachedObjectsARB must be different from glGetAttachedShaders,
since the pointers/ints are packed the output memory.