Fixed schema test for Oracle 11.2.0.1 which is used in Django Project's CI.

Refs #23073 Workaround.

Refs #22738 Repeats the mysql "offense". When the issue is solved, the
Oracle special case should be made to play with the solution (that is,
Oracle should be fixed the same way that mysql and the 3rd-party backneds
are).
Update squashmigration docs to also mention circ dep errs (refs #23337)
Added docstring forgotten in 56252e7.
Fixed #23343 -- Typo in docs/ref/class-based-views/generic-date-based.txt.
Fixed #23342 -- Clarified warning about naive time objects.

Thanks to apollo13 for suggested wording.
Fixed #23324 -- Mentioned Site.id in contrib.sites docs.
Fixed #23327 -- Added 'zero' syntax to migrate help message
Fixed #23167 -- Added BaseForm.__repr__()

Thanks Keryn Knight for the idea.
Tweaked docstrings from previous commit.
Fixed #23333 -- Made urlsafe_base64_decode() return proper type on Python 3.
Added new supported languages

Forward port of 46393980cf from stable/1.7.x
Fixed #22867 -- Memoized django.utils.version.get_git_changeset().

Restored original fix that had to be removed because the old djangoproject
server was still using Python 2.6.
Fixed #23344 -- Removed duplicate docs for file upload settings.
Replaced HAS_SPATIALREFSYS by a database feature
Replaced no_spatialite by connection features

Refs #22632. Thanks Tim Graham for the review.
Replaced no_mysql by connection features

Refs #22632. Thanks Tim Graham for the review.
Updated docs about Spatialite collect/extent support
Fixed #23352 -- Added tests for MigrationGraph.{forwards,backwards}_plan
Clarified release preparation step about dates.
Fixed #23341 -- Added migration name to nonexistent migration error in makemigrations.