* Test sanity cleanups
Partially addresses #87
- Remove manual lists of tests in favor of loadTestsFromName. This
mostly gets all test runners running the same number of tests.
- Remove `additional_tests`, which was just duplicating the discovered
tests. No modern test runner seems to need it.
- Change the two compatibility skip decorators to actually use
unitetest skips, which helps with the reporting.
* Per @tseaver, drop most test_suite functions.
* Port remaining doctest to unittest.
* Make the odd tests work on all supported python versions