Fixes a race condition in the documentation.

The example for django.contrib.admin.ModelAdmin.get_form was modifying self.exclude. However, since ModelAdmin instances are global and have no thread- or request-locality, this is not safe for concurrent requests. This updated documentation demonstrates a safe method to override admin forms on a per-request basis.

Fixed #23585 - Corrected internal comment.

Fixed #23690 - fixed examples of manual rendering of form fields

The example for django.contrib.admin.ModelAdmin.get_form modifies
self.exclude. However, since ModelAdmin instances are global and have no
thread- or request-locality, this is not safe for concurrent
requests.[1] This updated documentation demonstrates a safe method to
override admin forms on a per-request basis.

[1] https://groups.google.com/forum/#!topic/django-users/AmoUDtEefyA

Fixed #23808 -- Documented that migrations table is created when using runserver without migrating first.

Fixes #23837: Replace list with deque in migration-planner for improved performance.

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

Removed misleading comment and provide correct one, explaining
idea behind hardcoded CSRF template context processor.

Documentation for rendering form fields manually is now updated to use fields id_for_label instead of hardcoded values with additional mention of label_tag for alternative generation of complete label tag.

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