Message 247079 - Python tracker

Patch v15. No doc changes, but I refactored the test code:

* Manually merged with recent changes
* Separate assert_equality_only() and assert_total_order() test methods. Hopefully this is a bit simpler for people to understand and review, and avoids suggesting that partial ordering is tested.
* Dropped subTest() instances with identical parameters. The basic stack trace can already distinguish these.
* Eliminated is_value_comparable(); remove the ”meth” parameters from the call sites instead