Fixed #21142: Dependency failures on unmigrated apps.
Fix wording of auth superuser post-migrate handler
Fixed #21745 - Feature check UniqueTest.test_unique_null
Merge pull request #2150 from manfre/ticket-21745

Fixed #21745 - Feature check UniqueTest.test_unique_null
Fixed #21746 - Fixed test_get_reverse_on_unsaved_object test.

Test will no longer attempt to insert multiple NULL rows in to a unique
field if the database doesn't support it.
Merge pull request #2151 from manfre/ticket-21746

Fixed #21746 - Fixed test_get_reverse_on_unsaved_object test.
Make test stronger to hopefully fix odd Jenkins failure