Fixed #22359 -- Changing M2M field to blank=True failed on sqlite.
Fixed #22319 -- Fixed migration external dependencies when there are internal dependencies.
Fixed typo in docstring.
Added 1.6.3 release note for refs #22250.
Fixed #21795 -- Made add_preserved_filters account for url prefixes.

Thanks to trac username honyczek for the report. Refs #6903.
Replaced urllib/urlparse imports with from django.utils.six.moves.
Fixed #22362 -- Improved AuthenticationMiddleware assertion message.

Thanks Keryn Knight.
Fixed #22360 -- Fixed two non-deterministic tests in Python 3.4.

The order of admin's changelist filters in the querystring relied on
dict ordering.
Added test to confirm #12583 resolution
Fixed #22327 -- Turned BaseEmailBackend into a context manager

Changed the BaseEmailBackend to allow usage as context manager to open
and close connections.