Thanks Reinout van Rees for the review.

fixed #23834 -- added test and fix to check for default null on ArrayField

This commit broke the tests on Python 3.

This reverts commit 13d613f8.

Fixed #23827 -- TZ behavior in Storage API ref doc

Use topological sort for migration operation dependency resolution

rather than an ad-hoc algorithm

This is derived from the current behaviour of FileSystemStorage.
Note that since this was not previously documented, other
implementations may not currently conform.

Fixed #16358 - Made memcache backend delete old value on a failure to set.

The issue was fixed on master in e9103402
so this just forwardports the test and release notes from stable/1.7.x.

Forwardport of 2d12a599 from stable/1.7.x

Default Memcached configuration allows for a maximum object of 1MB and
will fail to set the key if it is too large. The key will be deleted from
memcached if it fails to be set. This is needed to avoid an issue with
cache_db session backend using the old value stored in memcached, instead
of the newer value stored in the database.

Custom form fields having a `queryset` attribute but no
`limit_choices_to` could no longer be used in ModelForms.

Refs #2445.

Thanks to artscoop for the report.

__init__ isn't allowed to return anything other than None and it isn't
common practice to include a return statement.

Thanks Baptiste Mispelon for review.

Usage of this method was removed pre 1.0 (c2ba59fc).

This fix is necessary for Python 3.5 compatibility (refs #23763).

Thanks Berker Peksag for review.

Made _do_update behave more strictly according to its docs,
including a corner case when specific concurent updates are
executed and select_on_save is set.

`io.open` is required on Python 2.7. Just `open` would work on Python 3.

JavaScript string extraction support has been added in gettext
0.18.3.
Thanks Aymeric Augustin for the review.

Added a test for the condition safe_join is designed to prevent.

Previously, a generic ValueError was raised. It was impossible to tell
an intentional exception raised to implement safe_join's contract from
an unintentional exception caused by incorrect inputs or unexpected
conditions. That resulted in bizarre exception catching patterns, which
this patch removes.

Since safe_join is a private API and since the change is unlikely to
create security issues for users who use it anyway -- at worst, an
uncaught SuspiciousFileOperation exception will bubble up -- it isn't
documented.