Fixed #23442 -- Added django.__version__ per PEP 396.

Thanks abhillman for the suggestion and Claude Paroz for review.
Avoid the word "stupid".

There's always a better word.
Fixed #22267 -- Fixed unquote/quote in smart_urlquote

Thanks Md. Enzam Hossain for the report and initial patch, and
Tim Graham for the review.
Fixed urlize after smart_urlquote rewrite

Refs #22267.
Note re migrations importing custom fields
Merge pull request #3208 from gregplaysguitar/master

Note re migrations importing custom fields
Fixed #23368 -- Overhauled the Welsh formats.py file.

The only debatable thing here is setting FIRST_DAY_OF_WEEK to 1.
The only examples of calendars I can find in Welsh start on Monday,
for example, the calendar on S4C (the only all Welsh TV station).

http://www.s4c.co.uk/clic/c_clicschedule.shtml
Fixed flake8 warnings.
Fixed an instance of 'an' before a word beginning with a consonant.
Fixed #23452 -- Prevented infinite migrations for empty unique/index_together.

Thanks fwkroon for the report.
Fixed #23417 -- Completed locale formats for zh_CN, zh_Hans, zh_Hant and zh_TW.
Corrected grammar in migrations error message.
Fixed #20743 -- Added support for keyfile/certfile in SMTP connections.

Thanks jwmayfield, serg.partizan, and Wojciech Banaś for work on the patch.
Fixed typo in topics/forms/formsets.txt
Corrected indentation in a contrib.humanize test; refs #23340.

Thanks Zach Borboa for the report.
Avoided using deprecated version of importlib; refs #23418.
Added some items to the 1.7.1 release notes.
Added ordering to prevent non-deterministic test failure; refs #23099.
Fixed #23403 -- Fixed crash in contrib.sitemaps if lastmod returned a date rather than datetime.

Thanks igorcc for the report.