CPython has this check. I think Pyston missed it when switch to the
CPython way of handling some inheritance functionality.

References:
CPython code:
https://github.com/python/cpython/blob/2.7/Objects/typeobject.c#L4074
Pyston commit that switch to the CPython way of handling it:
https://github.com/dropbox/pyston/commit/251f417abd68c4b018217ae3b1901b3f1687384d#diff-a5cc3ff8c761716ba33b328ad1d042dfR1499

And also add an extension for test.