This introduces TestCase.assertQueries(), a new unit test function

that can assert not just the number of queries performed by also the

complexity of those queries.
This takes in a list of queries built by Django and executed, checking

them for the lists of fields selected, tables joined, filter

conditions, annotations, ordering, and more.
This can offer a lot of advantages when writing tests, helping ensure

that queries are as performant as possible, or at least don't contain

unexpected complexity.

Made use of this in a bunch of unit tests in Review Board. Tested all

the major types of operations that can be performed when querying.