Handle case where seo_defaultmetadatamodel is created using 'loaddata'. ...

...The post_save callback should not be active, otherwise there is the potential for unique constraint violations with PostgreSQL DBs.

The test test_fallback_order2 currently fails, but I haven't found a combination of django and django-seo where it doesn't fail, either on Linux or Mac. Also, there are lots of test failures with 1.1.4<= and with >= 1.4, despite the docs saying django-seo is compatible with >= 1.1.