Fixed #16433 -- Fixed a help_text/read only field interaction that caused an admin crash.

Thanks chris at cogdon.org for the report and admackin for the patch.
Fixed #14786 -- Fixed get_db_prep_lookup calling get_prep_value twice if prepared is False.

Thanks homm for the report and Aramgutang and lrekucki for work on
the patch.
Fixed #20989 -- Removed explicit list comprehension inside dict() and tuple()

Thanks jeroen.pulles at redslider.net for the suggestion and
helper script.
Added links to file docs.
Fixed #20997 -- Added SessionStore note to docs.

Thanks jsdalton.
Added SplitHiddenDateTimeWidget to django.forms.widgets.__all__
Altered test introduced in f19a3669b8 for the sake of readability. refs #14786
Removed stale add_q() comment
Fixed #20988 -- Added model meta option select_on_save

The option can be used to force pre 1.6 style SELECT on save behaviour.
This is needed in case the database returns zero updated rows even if
there is a matching row in the DB. One such case is PostgreSQL update
trigger that returns NULL.

Reviewed by Tim Graham.

Refs #16649
Improved {% include %} implementation

Merged BaseIncludeNode, ConstantIncludeNode and Include node.

This avoids raising TemplateDoesNotExist at parsing time, allows recursion
when passing a literal template name, and should make TEMPLATE_DEBUG behavior
consistant.

Thanks loic84 for help with the tests.

Fixed #3544, fixed #12064, fixed #16147
Set 'bidi' Urdu property to True

Refs #20454.
Fixed #20989 -- Removed useless explicit list comprehensions.
Fixed #21005 -- Made schema tests language-independent

Thanks Simon Charette for the review.
Fixed #20999 - Allow overriding formfield class with choices, without subclass restrictions.

Refs #18162. Thanks claudep and mjtamlyn for review.
Fixed typo in docs/ref/models/options.txt
Fixed copy/paste error in measurement docs
Made the doc about translating string literals in templates more prominent.
Fixed #13182 -- Prevented trailing spaces in indented json output

Thanks Stéphane Raimbault for the report and the initial patch.
Properly skipped yaml tests when not installed
Made django.test.testcases not depend on staticfiles contrib app.

Do this by introducing a django.contrib.staticfiles.testing.StaticLiveServerCase
unittest TestCase subclass.

Fixes #20739.