pyloxi: add basic test cases for of11 and of12

Also fixes minor bugs when importing those modules, and adds a check-py target
to run all the unit tests against the generated code.
diff --git a/py_gen/templates/init.py b/py_gen/templates/init.py
index 4a14228..75d52be 100644
--- a/py_gen/templates/init.py
+++ b/py_gen/templates/init.py
@@ -30,7 +30,7 @@
 :: include('_autogen.py')
 
 import action, common, const, message
-:: if version >= 4:
+:: if version >= 3:
 import oxm
 :: #endif
 from const import *