[1.6.x] Noted that localmem is the default cache.

Backport of c456ea4ec8 from master
[1.6.x] Improved docs for ModelFormSet.clean().

Backport of 033b26173b from master
[1.6.x] Removed obsolete deprecation notes.
[1.6.x] Fixed #21488 -- Multiple locales treatment in i18n commands.

Removed multiple locales separated by commas variation (that wasn't
working as documented) in favor of simply allowing use of the
``--locale``/``-l`` options more than once for ``makemessages`` and
``compilemessages``.

Thanks Romain Beylerian for the report and Claude, Simon for their help.
[1.6.x] Fixed #21486 -- Prevented settings config in signal connection

This was particularly problematic in the chain get_wsgi_application
-> db.connections import -> signal connection -> settings configuration.
Thanks Jon Dufresne for the report.
Backport of 42fef294464 from master.
[1.6.x] Fixed #21490 -- Fixed custom admin URL reverse example.

Thanks glarrain for the report.

Backport of bfe7377adb from master
[1.6.x] Fixed typo in previous commit; refs #21490.

Backport of 03bc0a8ac5 from master
[1.6.x] Fixed #21507 -- Corrected default widget information for FileField

Backport of 70e61310d6 from master
[1.6.x] Fixed #21355 -- try importing _imaging from PIL namespace first.

Backport of 5725236c3e from master
[1.6.x] Fixed #21448 -- Fixed test client logout with cookie-based sessions

Thanks Gunnar Scherf for the report and the suggested patch.
Backport of 384816fcc from master.
[1.6.x] Fixed #21515 -- Corrected example of template.Context in documentation.

Thanks to trac user oubiga for the report.

Backport of 077af42139db84d88f293ab5eadc989a9169dce1 from master.
[1.6.x] Fixed #21496 -- Fixed crash when GeometryField uses TextInput

Thanks Rhett Garber for the report and initial patch.
Backport of 34b8a3855 from master.
[1.6.x] Fixed #21535 -- Fixed password hash iteration upgrade.

Thanks jared_mess for the report.

Backport of fddb0131d3 from master
[1.6.x] Fixed incorrect type for max_length.

Backport of 3b60ffa334 from master
[1.6.x] Fixed #21358 -- Allowed runserver on non-English locales

Thanks svartalf for the report.
Backport of 2080bce69 from master.
[1.6.x] Fixed #21538 -- Added numpy to test/requirements/base.txt

Thanks Tim Graham for the report

Backport of c75dd664cf from master
[1.6.x] Added a warning regarding risks in serving user uploaded media.

Thanks Preston Holmes for the draft text.

Backport of df6760f12c from master
[1.6.x] Added link to localized formatting doc from main index.

abb04f1f3f from master.
[1.6.x] Fixed #21558 -- Support building CHM files.

Thanks Michał Pasternak.

Backport of cd9e85ec from master.
[1.6.x] Listed 1.6.x releases in descending order

Backport of 0daa2f1bf1 from master