Fixed #12286 -- Modified the test case added in r12828 so that it passes under Postgres.

from django.conf import settings, Settings

from django.core.management import call_command

from django.db.models.loading import load_app

from django.test import TestCase

from django.test import TransactionTestCase

class ProxyModelInheritanceTests(TestCase):

class ProxyModelInheritanceTests(TransactionTestCase):

    def setUp(self):

        self.old_sys_path = sys.path