Follow up to 67d98441.

When both parent and child models had managers with the same name and
a migrations opt-in both were added to the migration state.

Thanks Tim for the review.

Thanks Josh for the amazing testing setup and Tim for the review.

It should help catch bugs.

Thanks Tim Graham for the review.

This removes the dependency of the Index class on its model attribute
when a name is passed to it.

Thanks to Markush for discussions.

Thanks to Markush for discussions.

In the case of multiple-table inheritance models, get_all_related_objects() and
get_all_related_objects_with_model() don't return the auto-created
OneToOneField, but the new examples didn't account for this.

alter_index_together and alter_unique_together no more use _remake_table method in sqlite3

Factor method signatures in test_autodetector to avoid clashing keyword
arguments when introducing indexes.