Fix compatibility with Django 1.5.

Django 1.5 introduced some new variables in Meta that the database
operations depended on, which Django Evolution didn't provide. These
variables are 'index_together' and 'swapped'. Both are now added and
given their defaults.

It also changed how constraint names were computed, breaking tests.
This is now fixed by abstracting out constraint name computation.

Fixes bug #136.
Log failed SQL statements during unit tests.

It can be hard to debug the unit tests when things go wrong. This helps
a bit by providing a log of the batch of SQL statements triggering the
failure, and the failure message.