Use a polyfill for Enum on Python<3.4

src/requirements.txt

@@ -11,6 +11,10 @@ html5lib
 slimit
 lxml
 
+# Polyfill for Python <3.4
+# Remove this, when Python 3.3 support is dropped
+flufl.enum
+
 # Debugging requirements
 django-debug-toolbar
 

src/tixlbase/plugins.py

@@ -1,4 +1,7 @@
-from enum import Enum
+try:
+    from enum import Enum
+except ImportError:
+    from flufl.enum import Enum
 
 from django.apps import apps