Fix spying on methods on old-style classes.
Review Request #10199 — Created Oct. 6, 2018 and submitted
On Python 2.6 and early versions of 2.7,
used on old-style classes (those not inheriting from
meant that some spies would succeed on some versions of Python and fail
We now fall back to simply modifying the dictionary in these cases.
Unit tests pass on all supported versions of Python.