Use PostgreSQL instead of MySQL

[aebrer]

From OSL:

As a result of the upgrade to Django 1.6, a limitation in MySQL has been exposed. When multiple records are inserted simultaneously the database deadlocks and refuses both records. This happens often as a result of our multiprocessing. There are two ways to mitigate this issue: one is to retry inserts that fail, another is to use another database engine that doesn't have this problem, such as PostgreSQL.
Most of the transition is easy. They speak slightly different dialects of SQL, which makes the aggregates a little hairy. I will be revisiting the old documentation to see if there are any references to how the tests were written, in hopes of being better able to judge the impact of my changes.