Improve tests to cover slicing scenarios that could be handled in unique
ways by 3rd party database backends.

ChoiceFieldRenderer was not rendering nested choices. Added recursion
to ChoiceFieldRenderer to take nested choices and render them as
<ul>'s.

Added it to the settings reference. We used to have it in comment form
in our old, bigger default project template settings.py file.

Code had been added in e909ceae. Solves test suite failures observed
on Windows.

Thanks Michael Manfre for the report. Refs #20739.

The import was done from util instead of utils leading to
PendingDeprecationWarning.

Thanks to onlygoldi2201 for the report and to ramiro and apollo13
for the reviews.

Also fixed a py3 incompatibility.
Thanks to brutasse for the report.

I a word :-/

DatabaseCache uses raw cursors to bypass the ORM. This prevents it from
being used by database backends that require special handling of datetime
values.

There is no easy way to test this, so no tests added.

Thanks to EmilStenstrom for raising this, and to Chris Piwoński for all of the fixes and most of the tests.

A .annotate().select_related() query resulted in misaligned rows vs
columns for compiler.resolve_columns() method.

Report & patch by Michael Manfre.

The commit for #18333 missed quote_cache default value for *.
Refs #18333.

Thanks go to Michael Gebetsroither for pointing out this issue and help on
the patch.

This reverts commit aae5a96d.

This fix is no longer necessary, our pbkdf2 (see next commit) implementation
no longer rehashes the password every iteration.

Thanks marfire for the report.

Fixed #21152: Corrected small grammatical error in comment.

Changed 'there are no filtering' to 'there is no filtering'.

This change prevents including the multiple_database test models without
duplicating the router code (we probably should do this at one point).

Refs #21148