Fixed Python 2.6 tests, and fixed tox.ini from PR #162 for python 3

polymorphic/tests.py

@@ -6,7 +6,7 @@ from __future__ import print_function
 import uuid
 import re
 import django
-from unittest import skipIf
+from django.utils.unittest import skipIf
 from django.db.models.query import QuerySet
 
 from django.test import TestCase

tox.ini

@@ -2,9 +2,10 @@
 envlist=
     py26-django{14,15,16},
     py27-django{14,15,16,17,18},
-    py32-django{14,15,16,17,18},
-    py33-django{14,15,16,17,18},
-    py34-django{14,15,16,17,18},
+    py32-django{15,16,17,18},
+    py33-django{15,16,17,18},
+    py34-django{15,16,17,18},
+    # py33-django-dev,
     docs,
 
 [testenv]