Exclude Guardian testing against Django master

tox.ini

@@ -39,3 +39,25 @@ commands = mkdocs build
 deps =
        -rrequirements/requirements-testing.txt
        -rrequirements/requirements-documentation.txt
+
+# Specify explicitly to exclude Django Guardian against Django master (various Pythons)
+[testenv:py27-djangomaster]
+deps =
+       https://github.com/django/django/archive/master.tar.gz
+       -rrequirements/requirements-testing.txt
+       markdown==2.5.2
+       django-filter==0.10.0
+[testenv:py34-djangomaster]
+deps =
+       https://github.com/django/django/archive/master.tar.gz
+       -rrequirements/requirements-testing.txt
+       markdown==2.5.2
+       django-filter==0.10.0
+
+[testenv:py35-djangomaster]
+deps =
+       https://github.com/django/django/archive/master.tar.gz
+       -rrequirements/requirements-testing.txt
+       markdown==2.5.2
+       django-filter==0.10.0
+