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/message.py b/py_gen/templates/message.py
index 69c3fe1..de8fb86 100644
--- a/py_gen/templates/message.py
+++ b/py_gen/templates/message.py
@@ -217,7 +217,11 @@
     const.OFPST_TABLE : table_stats_reply.unpack,
     const.OFPST_PORT : port_stats_reply.unpack,
     const.OFPST_QUEUE : queue_stats_reply.unpack,
+:: if version < of_g.VERSION_1_1:
     const.OFPST_VENDOR : experimenter_stats_reply.unpack,
+:: else:
+    const.OFPST_EXPERIMENTER : experimenter_stats_reply.unpack,
+:: #endif
 }
 
 stats_request_parsers = {
@@ -227,7 +231,11 @@
     const.OFPST_TABLE : table_stats_request.unpack,
     const.OFPST_PORT : port_stats_request.unpack,
     const.OFPST_QUEUE : queue_stats_request.unpack,
+:: if version < of_g.VERSION_1_1:
     const.OFPST_VENDOR : experimenter_stats_request.unpack,
+:: else:
+    const.OFPST_EXPERIMENTER : experimenter_stats_request.unpack,
+:: #endif
 }
 :: else: