Adding smoke test for #29, running migrations always fails if there is a SortedM2M in use. Even if it's not part of the migration.
Updating create_sorted_many_to_many_intermediate_model to support django 1.7 app registry.
Testing django 1.7 migrations.
Updating tox file.
Make SortedManyToManyField run under Django 1.5, 1.6 and 1.7 including migrations.