Update to Django 1.6
Fix JSON serialization of visited_instances

OrderedDicts get JSON serialized as regular dictionaries, so the
de/serialization process was causing a type error.

Instead, we just convert to and from OrderedDict and store as a simple
but readily compatible type, lists of tuple pairs.
Add fabric command to check django settings
Fix pesky migrator messages in unit test output
Merge pull request #1444 from steventlamb/topic/upgrade_to_1.6

Topic/upgrade to 1.6