This removes the concept of equality between operations to guarantee
compatilibity with Python 3.
Python 3 requires equality to result in identical object hashes. It's
impossible to implement a unique hash that preserves equality as
operations such as field creation depend on being able to accept
arbitrary dicts that cannot be hashed reliably.
Thanks Klaas van Schelven for the original patch in
13d613f800.
This inspects the migration operation, and if it is not in the
django.db.migrations module, it adds the relevant imports to the
migration writer and uses the correct class name.
