Issue #1717: rename tp_compare to tp_reserved.  I'll change the
type of tp_compare in a separate commit, for ease of reversion
should things go wrong.
diff --git a/Objects/memoryobject.c b/Objects/memoryobject.c
index 0b65d44..0f7d71d 100644
--- a/Objects/memoryobject.c
+++ b/Objects/memoryobject.c
@@ -805,7 +805,7 @@
     0,                                        /* tp_print */
     0,                                        /* tp_getattr */
     0,                                        /* tp_setattr */
-    0,                                        /* tp_compare */
+    0,                                        /* tp_reserved */
     (reprfunc)memory_repr,                    /* tp_repr */
     0,                                        /* tp_as_number */
     0,                                        /* tp_as_sequence */