This adds a test for database upgrades, which I developed on a branch
that added a new DB schema (v3) and an upgrader to match, but then I
changed my mind about the schema and removed that part. The test will be
useful some time in the future when I change the schema in a small
enough way that I bother to write an upgrader for the change. For now,
the test is disabled.
In addition, the upgrader test is kind of lame. I'd really prefer to
assert that the upgraded schema is identical to the schema of a
brand-new (latest-version) database, but ALTER TABLE doesn't quite work
that way (comments are omitted, and the order of the columns is slightly
different).
This also adds database.dump_db() for the tests.
