If I understand Christian's plan correctly, it was to:
(1) raise TypeError for non-NULL tp_compare, and
(2) rename tp_compare to tp_reserved (with type void *).
and both of these would happen with 3.0.1, so no difference between
3.0.1 and 3.1.0.
It seems to me that if tp_compare is actually going to be removed then
that should be done in 3.0.1; else third-party stuff that works with
3.0.x will fail with 3.1, due to the various tp_* fields being out of sync.
It would be nice not to have tp_reserved hanging around for the duration
of 3.x. (Similarly for nb_reserved.)