[1.7.x] Fixed #22417 -- Added additional documentation for refs #16969.

Thanks Jon Foster for the report.

Backport of 1b3a3fc1e4 from master
[1.7.x] Fixed flake8 errors.

Backport of 471fb04a30 from master
[1.7.x] Fixed flake8 warnings introduced in recent commits.

Backport of 79f05616fbf48cf7c205ef17666af0c3d47b3c1e from master
[1.7.x] Fixed #22402 -- Consolidated model_inheritance tests.

The model_inheritance_same_model_name tests couldn't be run without the
model_inheritance tests. Make the problem go away by merging them.

Thanks timo for the report.

Backport of 0097d38 from master
[1.7.x] Further consolidated the model_inheritance tests.

Backport of 3f01e82 from master
[1.7.x] Corrected many style guide violations that the newest version of flake8 catches

Backport of 778ce245dd466bce1b19f89e52cf9ed8f1b46513 from master
[1.7.x] Appeased flake8 2.1.0.

Backport of 428c0bbe1bcd303560d7e96d7d2721ff3fdc0e3f from master
[1.7.x] Fixed monkeypatching in a staticfiles test.

Backport of a4553e0510 from master
[1.7.x] Corrected the section identifier for MySQL unicode reference.

Backport of b2514c02e1 from master
[1.7.x] Fixed a remote code execution vulnerabilty in URL reversing.

Thanks Benjamin Bach for the report and initial patch.

This is a security fix; disclosure to follow shortly.

Backport of 8b93b31487d6d3b0fcbbd0498991ea0db9088054 from master
[1.7.x] Prevented leaking the CSRF token through caching.

This is a security fix. Disclosure will follow shortly.

Backport of c083e3815aec23b99833da710eea574e6f2e8566 from master
[1.7.x] Fixed queries that may return unexpected results on MySQL due to typecasting.

This is a security fix. Disclosure will follow shortly.

Backport of 75c0d4ea3ae48970f788c482ee0bd6b29a7f1307 from master
[1.7.x] Added information on resolved security issues to release notes.

Backport of c07f3e60c2d455e36ba4ac339d4283d32bbc3814 from master
[1.7.x] Update for 1.7b2 security release.