TestModelsLoaderMixin attempted to set up some initial state for a

test suite, and then manage the database state per-test. The way it did

this made some bad assumptions that held up in earlier versions of

Django and with older versions of Django Evolution, but weren't quite

correct, and fails with Django Evolution 2.1.
The old code tried to perform a migrate at the start of each test, and

a flush at the end. These were often being done within a transaction

(set up by TestCase.setUpClass()), which currently fails with Django

Evolution (since it cancels the upgrade if in a transaction) and would

fail with Django's own migrate if run on MySQL (for the same reason).
The new code has been reworked to perform all the necessary operations

within setUpClass()/tearDownClass(), outside of any transaction

management. This allows us to populate the database up-front, enter a

transaction, and roll it back per-test, rather than flushing the whole

database per-test.
A huge benefit is that there's a major performance gain for many of our

unit tests, dropping it from 90 seconds to 18 seconds on my local

machine.

All unit tests pass.