[1.5.x] Fixed test failures introduced in a5becad9094e5c5403b692b9a7b3a6ffaabf64a3.

Backport of 780fa48f5fb81b2f0f58de95167abff84a6149aa from master
[1.5.x] Fixed #20305 - Added include for polls/static to MANIFEST.in in tutorial.

Thanks monuszko for the report.

Backport of 86d3079d57 from master
[1.5.x] Fixed #20274 - Added some clarifying section headings in the test docs.

Backport of e886808994 from master
[1.5.x] Fixed #20177 - Corrected docs for django.test.utils.setup_test_environment.

Thanks vlad.london.uk@ for the report.

Backport of bc02a963db from master
[1.5.x] Fixed #20354 -- `makemessages` no longer crashes with `UnicodeDecodeError`

Handle the `UnicodeDecodeError` exception, send a warning to `stdout` with the
file name and location, and continue processing other files.
Backport of 99a6f0e77 from master.
[1.5.x] [py3] Stopped iterating on exceptions. Refs #20025.

Backport of 86b4ac66 from master.
[1.5.x] Fixed #20025 -- Pointed to a MySQLdb fork for Python 3.

Made a few minor compatibility adjustments.

Backport of e81e319f from master.
[1.5.x] Fixed #20385 -- Typo in files docs.

Backport of bdd2857 from master.