Implement initial migration detection
|Reported by:||timo||Owned by:||andrewgodwin|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
Currently documented functionality in topics/migrations is not implemented: "This will make a new initial migration for your app. Now, when you run migrate, Django will detect that you have an initial migration and that the tables it wants to create already exist, and will mark the migration as already applied."
On SQLite, for example, you get this traceback: django.db.utils.OperationalError: table polls_poll already exists