Fixed #22116 -- Added precision about WSGIPythonPath separator

Thanks donjpacheco for the initial patch.
Fixed #22142 -- Documented PostGIS 2 database creation during tests
Fixed docs typos.
Fixed #22071 -- Added a warning regarding override_settings and aliasing.

Thanks EvilDMP for the suggestion.
Fixed #12670 -- Added a note about permissions of files stored in FILE_UPLOAD_TEMP_DIR.

Thanks simon29 for the suggestion.
Removed a nonexistent link in the docs.
Fixed #22145 -- Clarified docs on Field.blank and Field.null options.

Thanks skipjack at peru.com for the suggestion.
Fixed bad grammar in a comment.
Fixed #21389 -- Accept most valid language codes

By removing the 'supported' keyword from the detection methods and only relying
on a cached settings.LANGUAGES, the speed of said methods has been improved;
around 4x raw performance. This allows us to stop checking Python's incomplete
list of locales, and rely on a less restrictive regular expression for
accepting certain locales.

HTTP Accept-Language is defined as being case-insensitive, based on this fact
extra performance improvements have been made; it wouldn't make sense to
check for case differences.
Fixed #22056 -- Omitted non-package directories when collecting tests

This allows us to ignore empty dirs or other unrelated dirs.
Thanks Sebastian Pawluś for the report and the initial patch.
Fixed documention typo
Merge pull request #2374 from spaceexperiment/doc_typo

Fixed documention typo
Fixed #22136 -- Updated comment for Textarea widget

Thanks Aymeric Augustin for the suggestion.
Replaced deprecated assertEquals
Fixed #21962 -- Added escape_html flag to ErrorDict.as_json()
Removed Django 1.5 upgrade hints for {% url %} tag.

Refs #19280 and Refs #19392.
Fixed #22129 -- Added steps for creating superusers to tutorial.
Fixed #22028 -- Documented that database signals aren't emitted for apps that laack a models module.

Thanks un33k for the suggestion and donjpacheco for the draft patch.
Fixed doc typos.
Fix keyword agument names in RunPython to be positional