The fixtures that we were autousing needed to be used explicitly, to
get randomly-generated dataset names.  One was only used for one test.

Also, fixed copyright.

We don't require alembic and most tests should run without it, however

- We run some unit tests (Python 3.8) to cover the alembic
  registration that happens when alembic is installed.

- We have a system test that demonstrates working with alembic and
  proves that the things we think should work do work. :)