The per-database unit test data modules now pass a connection for the

appropriate database type to the functions used to generate index names.

This will be required for Django 1.11, which will have logic that's more

connection-dependent.
To do this, we now have our own test_connections that works like

django.db.connections, but is based on the unit test databases. This

is needed because those databases are not registered in

settings.DATABASES (since that would otherwise require each database

to be set up and would register tables in each). Each of the database

data modules now make use of this instead of assuming that

django.db.connection matches the correct database type.

Unit tests pass on Django 1.6 through 1.10 with all database types.