[1.6.x] Fixed #21625 -- incorrect documentation for DiscoverRunner.build_suite

Backport of b62031441b2e1cb1eeb7e1d6f254c553643add96 from master.
[1.6.x] Fixed #21632 -- Docs: Removed example with callable as query parameter

Using callables as query parameters is undocumented and not working,
so this changes an example from the ForeignKey.limit_choices_to
documentation that uses it.

Backport of d34c8c338a from master
[1.6.x] Fixed #21613 -- Removed a hardcoded input id from the tutorial.

Thanks Bruno Brouard for the report.

Backport of cc2d960274 from master
[1.6.x] Fixed #21585 -- Updated some links to 3rd party database projects.

Thanks graeme.perrow at sap.com for the original report.

Backport of 23d9f517dc from master
[1.6.x] Fixed #21213 -- Added docs for Django's mailing lists.

Added docs/internals/mailing-lists.txt documenting the use of django's
mailing lists. All references across docs changed to point to this page.

The referencing makes use of substitution because there's no way to make
a :ref: link in a non-inline fashion in Sphinx. It also makes use of
rst_epilog Sphinx conf for making this substitutions across all the
docs.

Backport of 3895d8899d from master
[1.6.x] Fixed #21663 -- Added missing WSGIPythonPath in mod_wsgi config.

Thanks carrie.hazelton at altamiracorp.com for the report.

Backport of e82e7ae1e8 from master
[1.6.x] Fixed #21662 -- Kept parent reference in prepared geometry

Thanks Robert Scott for the report.
Backport of 542198c1d0 from master.
[1.6.x] Fixed #21627 -- Added unicode_literals to changepassword command.

Fixed a crash when executing changepassword command when the user object
representation contained non-ASCII characters.

Backport of 398642fd9b from master
[1.6.x] Fixed typo and slightly improved error message when db is missing time zone definitions.

Refs #21432.

Backport of 32e75803be from master
[1.6.x] Fixed #21629 -- Added instructions for loading MySQL time zone definitions.

Thanks Aymeric for the suggestion.

Backport of d8d83777eb from master
[1.6.x] Fixed #21582 -- Corrected URL namespace example.

Thanks oubiga for the report.

Backport of 025ec2e7fe from master
[1.6.x] Fixed #21650 -- Corrected bad advice for plural translation.

Thanks nedbatchelder and claudep.

Backport of 85270ef3f5 from master
[1.6.x] Fixed #21618 -- Added hints about openlayers.js hosting

Thanks kz26 for the report and Tim Graham for the excellent
review.
Backport of b7a7baa554 from master.
[1.6.x] Fixed #21093 -- Ensured that mails are not base64 encoded on python 3.3.3+.

Thanks to Arfrever for the report and Aymeric for the review.

Backport of f28ea0230846c81e9b6725454bb3a10df24678aa from master.
[1.6.x] Worked around a bug in python 3.3.3. Refs #21093

Backport of 280c1a65ccacd679bf298bf2b169ff01e7266b8e from master.
[1.6.x] Fixed #21710 -- Documented User.get_short_name()

Thanks Keryn Knight for the report.

Backport of 0150830687 from master
[1.6.x] Fixed #21708 -- Added some headings to separate unrelated topics.

Thanks ashley at ashleymills.com for the suggestion.

Backport of 270f7e2167 from master
[1.6.x] Introduced as_bytes for SafeMIMEText (and other SafeMIME-classes).

This is to provide a consistent interface (namely bytes) for the smtp
backend which after all sends bytes over the wire; encoding with as_string
yields different results since mails as unicode are not really specified.

as_string stays for backwardscompatibilty mostly and some debug outputs.
But keep in mind that the output doesn't match as_bytes!

Backport of 5dfd824d38ec7d1f695494e46d603e89cae68661 from master.
[1.6.x] Changed console and filebackend to use msg.as_bytes to output the data as it would get send via smtp.

Backport of c988745cca1225496bfd36910dc3cec5065d8cc4 from master.
[1.6.x] Decode mails using the message encoding.

Backport of bfe9052831c6d7ad7501b71c884525b3b471eebc from master.