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
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.
Renamed qn to compiler
Added reminder to committing docs to test a PR with Jenkins first.
Fixed #21612 -- Made QuerySet.update() respect to_field
Fixed regression in 4dc4d12e. Refs #21598.

That commit contained a mistake that resulted in the use_cached_loader
option of override_with_test_loader being ignored. As a consequence some
configurations weren't exercised any more by the test suite.
Moved all template loaders under django.template.loaders.

Reformatted the code of base.Loader according to modern standards.

Turned the test template loader into a regular locmem.Loader -- but
didn't document it.

Added a normal deprecation path for BaseLoader which is a public API.

Added an accelerated deprecation path for TestTemplateLoader which is
a private API.