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

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.
Fixed #23585 - Corrected internal comment.

Removed misleading comment and provide correct one, explaining
idea behind hardcoded CSRF template context processor.
Revert "Use topological sort for migration operation dependency resolution"

This commit broke the tests on Python 3.

This reverts commit 13d613f80011852404198dfafd1f09c0c0ea42e6.
added test and fix to check for default null on ArrayField
Fixed #23793 -- Clarified password reset messages.
Fixes #23837: Replace list.pop(0) by deque.popleft() in dfs function in migrations
Merge pull request #3531 from ddaan/ticket_23834

fixed #23834 -- added test and fix to check for default null on ArrayField
Refs #23793 -- Fixed test failure after password reset messages clarification
Fixed #23835: Changed circular dependency in DFS to be less infinite
Fixed #23793 -- Clarified password reset behavior in auth docs
Added a new GeoJSON serialization format for GeoDjango

Thanks Reinout van Rees for the review.
Merge pull request #3536 from Zweedeend/ticket_23837

Fixes #23837: Replace list with deque in migration-planner for improved performance.
Fixed #23825 -- Added links for decorating class-based views to the CSRF docs.
Fixed #21363 -- Added datetime.timedelta support to TimestampSigner.unsign().
Added tests/README.rst
Fixed #23808 -- Documented that migrations table is created when using runserver without migrating first.
Fixes a race condition in the documentation.

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
Removed old version note in layermapping.txt
Removed references to the deprecated assertRaisesRegexp method.
Designated Django 1.8 as the next LTS.