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.)