Fixed two older bugs in introspection inspectdb.
Fixed two older bugs in introspection inspectdb.

* The command inspectdb raised exception if 'salesforce' is was not
  in INSTALLED_APPS
* Unique fields (with Unique checkbox checked) were not marked by "unique=True".

django-salesforce/django-salesforce,hynekcer/django-salesforce,hynekcer/django-salesforce,hynekcer/django-salesforce,django-salesforce/django-salesforce,django-salesforce/django-salesforce