A Mystery:  test_mutants ran amazingly slowly even before dictobject.c
"got fixed".  I don't have a clue as to why.  dict comparison was and
remains linear-time in the size of the dicts, and test_mutants only tries
100 dict pairs, of size averaging just 50.  So "it should" run in less than
an eyeblink; but it takes at least a second on this 800MHz box.