Django-ddp

------------------
* Add dddp.accounts module which provides password based auth mapping to
django.contrib.auth module.
* Fix ordering of change messages and result message in method calls.

------------------
* Drop relations to sessions.Session as WebSocket requests don't have
HTTP cookie support -- **you must `migrate` your database after
upgrading**.
* Refactor core to support custom serialization per collection, and
correctly dispatch change messages per collection.
* Allow specifying specific collection for publication queries rather
than assuming the auto-named default collections.
* Improve schema introspection to include options for fields with
choices.
* Cleanup transaction handling to apply once at the entry point for DDP
API calls.

------------------
* Make live updates honour user_rel restrictions, also allow superusers
to see everything.
* Support serializing objects that are saved with F expressions by
reading field values for F expressions from database explicitly before
serializing.
* Allow `fresh` connections from browsers that have not established a
session in the database yet, also allow subscriptions from
unauthenticated sessions (but don't show any data for collections that
have user_rel items defined). This change includes a schema change,
remember to run migrations after updating.

------------------
* New DB field: Connection.server_addr -- **you must `migrate` your
database after upgrading**.
* Cleanup connections on shutdown (and purge associated subscriptions).
* Make `dddp` management command a subclass of the `runserver` command
so that `staticfiles` work as expected.
* Fix non-threadsafe failure in serializer - now using thread local
serializer instance.
* Fix `unsubscribe` from publications.
* Fix `/schema` method call.

------------------
* Fix foreign key references in change messages to correctly reference
related object rather than source object.

------------------
* Fix unicode rendering bug in DDP admin for ObjectMapping model.