Revert "Fixed South migrations. Refs #593"

This reverts commit 42e3334ef805eb50bc0429b6faf6f7b99c1e47a3.
Hack around custom user model
Merge branch 'issue593' of git://github.com/oinopion/django-social-auth into oinopion-issue593
Freeze model in case no migration is defined. Refs #593
Small line to shutup pyflakes