updated tox file for python 3.3

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py26,py27
+envlist = py26,py27,py33
 
 [testenv]
 deps =
@@ -10,3 +10,11 @@ commands =
     coverage run --source=icalendar --omit=*tests* {envbindir}/unit2 discover icalendar []
     coverage report --omit=*tests*
     coverage html --omit=*tests*
+
+
+[testenv:py33]
+basepython = python3.3
+deps =
+	unittest2py3k
+	coverage
+