Add middleware to test_settings to remove warning in django 1.7.
Add middleware to test_settings to remove warning in django 1.7.

happylyang/django-adminplus,deannariddlespur/django-adminplus,happylyang/django-adminplus,drdaeman/django-adminplus,deannariddlespur/django-adminplus,drdaeman/django-adminplus,deannariddlespur/django-adminplus,drdaeman/django-adminplus,happylyang/django-adminplus