Added check for nonrel db type.
Added check for nonrel db type.

emergence/django-simple-history,emergence/django-simple-history,luzfcb/django-simple-history,treyhunner/django-simple-history,treyhunner/django-simple-history,pombredanne/django-simple-history,luzfcb/django-simple-history,pombredanne/django-simple-history