More robust version handling: Keep versions aligned.

[thorwhalen]

We've had problems with versions (the opinion of tags, setup.cfg, and pypi) getting misaligned and causing havoc.

Good-enough solutions were implemented, but these are more to enable us to diagnose the problem (#11) and circumvent it (#29).

This issue is meant to diagnose the problem further, to see what kind of use actions lead to misalignment in the first place, and solution the problem at that level.