Postgresql backend uses implicit text casts for case insensitive operators

[Ubercore]

In django.db.backends.postgresql.operations.DatabaseOperations, a case insensitive lookup produces

UPPER(%s::text)

as the lookup cast sql.

In django.db.backends.postgresql.DatabaseWrapper.operators, a case insensitive lookup produces

UPPER(%s)

Since Postgres 8.3 removed implicit casts, all operators should use ::text. Not doing so breaks lookups that use a type other than text:

AModel.objects.filter(col1__iexact=4)

[Ubercore]

Changing to 1.2 milestone, as this seems like a low impact bugfix.

[James Bennett]

Since iexact doesn't make sense for non-text lookups, I don't think this is critical enough to be on the 1.2 milestone right now.

[Julien Phalip]

The tests would need to be rewritten using unittests since this is now Django's preferred way.

[kwadrat]

This ticket can be closed because it is already implemented in: django/db/backends/postgresql_psycopg2/operations.py, class DatabaseOperations, method lookup_cast

[kwadrat]

Waiting for review.

[Claude Paroz]

Test committed in [d902fd625d11bd8a69c3a26b5ed90eefa38d2f6d].