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.
Fixes #23837: Replace list.pop(0) by deque.popleft() in dfs function in migrations
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.
Merge pull request #3524 from nmundar/ticket_23690

Fixed #23690 - fixed examples of manual rendering of form fields
Merge pull request #3526 from gregorth/ticket_23585

Fixed #23585 - Corrected internal comment.
Merge pull request #3549 from psagers/master

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.
Added reminder to committing docs to ask Jenkins test a PR.