pat-checkedflag, issue #381

Fix an issue where the pattern does not behave as designed for radio buttons, depending on their order.
The tests should have caught this, but did not, because they were testing `_onChangeCheckbox` instead of `_onChangeRadio`.  So I fixed the tests, and added more, to account for different permutations in the order of two and three radio buttons.
Unfortunately, due to issue #387, I can't actually run the tests.
This looks incorrect at first sight: if the button is not checked we may need to reset existing classes that should not be present.