Added python3.3 environment to the envs to test in tox.ini

tox.ini

 [tox]
-envlist = py27-django14, py27-django15, py27-django16
+envlist = py27-django14, py27-django15, py27-django16, py33-django16
 
 [testenv]
 commands = ./runtests.py
@@ -32,3 +32,9 @@ basepython = python2.7
 deps =
      Django==1.6.1
      {[testenv]deps}
+
+[testenv:py33-django16]
+basepython = python3.3
+deps =
+     Django==1.6.1
+     {[testenv]deps}