(Django v1.5) confirm method removed from BaseDatabaseFeatures

Hello!

On Django trunk, cached properties now keep track of database features like transaction support (https://github.com/django/django/commit/aa423575e7b464433fcfc4bf4b8e1d7627b17ce6).

Because the confirm method was removed, attempting to run django-nose tests with `REUSE_DB=1` generates an obscure `'SkipDatabaseCreation' object has no attribute '_rollback_works'` AttributeError.

See patch for workaround. And thanks for your work on django-nose!