Adds generators support for email backends that do not support it.
Fixed #20404 -- Added a keys() method to ContextList.

It's useful to be able to list all the (flattened) keys of a
ContextList, to help you figure out why the variable that's supposed
to be there is not.

No .values() or .items() added as the definition for those aren't clear.

The patch is Chris Wilson's patch from pull request 1065 with some
modifications by committer.
Fixed #18785 -- Added Test join trimming regression

The regression was caused by patch to ticket #15316 and was fixed by a
patch to #10790.
Fixed #18169 -- NoReverseMatch not silenced if from block.super
Fixed #18481 -- Wrapped request.FILES read error in UnreadablePostError

Thanks KyleMac for the report, André Cruz for the initial patch and
Hiroki Kiyohara for the tests.
Fixed #20543 - Typo in db model fields docs.

Thanks i.amber.jain@ for the report.
Fixed #20540 -- Added more translatable strings to contrib.admindocs

Thanks lborgav for the initial patch.
Updated contrib.admindocs translation template
Changed assertEquals -> assertEqual.
Added minor splitting optimization in django.utils.ipv6._unpack_ipv4
Fixed #20337 -- Clarified error message when database relation is not allowed.
Fixed #18388 - Added InlineModelAdmin.get_max_num hook.

Thanks d.willy.c.c@ for the suggestion and Melevir and Areski Belaid for work
on the patch.
Fixed admindoc template errors introduced by 02fd87c821.

Also regenerated the affected translation template.

Refs #20540.
Switched to using some constants the hmac module exposes.
Added get_app_paths() to the AppCache.

This method is useful to discover files inside apps.
Fixed #20485 -- Refactored loaddata for speed.

Thanks Anssi for reporting this performance bottleneck.
Fixed #20552 -- Corrected release notes reference to name of new test discovery runner.
Fixed small regression from 51aa000378.

A test failed if the path to the Django checkout contained a dot.

Refs #20485.
Fixed loaddata for Django checkouts with non ASCII chars in the name.
Fixed #20545 - Made class-based view MRO lists consistent.

Thanks wim@ for the suggestion.