Fixed #20598 -- Add new HTTP status codes defined in rfc6585

428, 429, 431 and 511
Fixed #20528 -- regression in select_related join promotion

The join used by select_related was incorrectly INNER when the query
had an ORed filter for nullable join that was trimmed away. Fixed this
by forcing the join type to LOUTER even when a join was trimmed away
in ORed queries.
Fixed python 3.2 compat.
Added cache to available_apps in cache tests
Fixed #20289 -- pickling of dynamic models
Fixed #20565 -- Added template examples for GCBV.

Thanks to David Reitter for the report,
and to Marc Tamlyn and Baptiste Mispelon for the review.
Fixed #20548 -- Removed all PendingDeprecationWarnings from django test suite
Merge pull request #1272 from chicheng/addition-http-status-codes

Fixed #20598 -- Add new HTTP status codes defined in rfc6585
Merge pull request #1271 from batisteo/ticket-20565

Fixed #20565 -- Added template examples for GCBV.