[1.7.x] Fixed #22426 -- Added support old-style d.c.messages format.

Forward ported code from 1.5 that adds backwards compatibility with legacy message length.
See commit 9e7183073f64e541587e8dcfd8bb3ddeb47f8162 for details.

Thanks to Ofir Ovadia for the initial patch.

Backport of f286721f7fdc2202f77a5f4d650d9d0779b86811 from master.
[1.7.x] Added 1.6.4 release note stub.

Backport of 9fb95dfc9f from master
[1.7.x] Fixed #22478 -- Regression in test label discovery.

As part of the app-loading updates the old test runner was changed to not
require a models module. This introduced a regression in behavior so
applabel.TestCase failed for tests defined in a directory.

The fix is thanks to yakky and rtnpro.
[1.7.x] Fixed adding new GIS column in PostGIS 1.x migration

Refs #22451.
Backport of fb09a489c from master.
[1.7.x] Fixed removal of GIS column in PostGIS 1.x migration

Refs #22481.
Backport of 2f9d1576e from master, squashed with 2f9d1576e8.
[1.7.x] Fixed table cleanup in GIS migration tests

Backport of ab90c4707b from master.
[1.7.x] Updated grammar in description of django.contrib.auth.

Backport of 9853779805 from master
[1.7.x] Various documentation typo/spelling fixes

Errors detected by Topy (https://github.com/intgr/topy), all changes
verified by hand.

Backport of 11d453bcad from master