Thanks Tim Graham and Markus Holtermann for review.

MigrationRecorder now assumes that if the django_migrations table
doesn't exist, then no migrations are applied.

Reverted documentation change from refs #23808.

In retrospect, implementing a __repr__() for index subclasses doesn't
seem worthwhile.

Fixed #27539 -- Made TransactionTestCase._pre_setup() clear the queries_log so it's less likely to overflow.

TransactionTestCase.assertNumQueries() fails in an overflow situation.

Thanks Tim Graham for the review and edits.

Mistake in 97c1931c.

Migrations will now be created for changes to limit_choices_to.