[1.5.x] Fixed #21121: Added archive of security issues.

Backport of 9d3e60a, 8e134c2, 8b3bae9, c65ae7c, bbabc53,
and a2e25e8 from master.
[1.5.x] Added __pycache__ to gitignore

Backport of 55b9bff07f from master
[1.5.x] Added missing "in" in sentence.

Backport of 2c5c422d34 from master
[1.5.x] Fixed #21133 -- Clarifed documentation about strftime formatting.

Backport of 43a2ec7999 from master
[1.5.x] Fixed #21137 -- Documented best practice for URLconfs with repeated pattern prefixes.

Backport of 222460a994 from master
[1.5.x] Correct very minor typo

Just changed as to has.

Backport of d8f2d940cc from master
[1.5.x] Fixed a couple of typos in GeoDjango docs.

8b366a50f4 from master.
[1.5.x] Reference Meta.index_together in DB performance guide.

9dc45efeba from master.
[1.5.x] Fixed "Address already in use" from liveserver.

Our WSGIServer rewrapped the socket errors from server_bind into
WSGIServerExceptions, which is used later on to provide nicer
error messages in runserver and used by the liveserver to see if
the port is already in use. But wrapping server_bind isn't enough since
it only binds to the socket, socket.listen (which is called from
server_activate) could also raise "Address already in use".

Instead of overriding server_activate too I chose to just catch socket
errors, which seems to make more sense anyways and should be more robust
against changes in wsgiref.

Backport of 2ca00faa913754cd5860f6e1f23c8da2529c691a from master
[1.5.x] Stopped a test from executing queries at the module level.

Currently module level queries are executed against the real database
(specified in NAME) instead of the test database; since it is to late
to fix this for 1.6, we at least ensures stable builds. Refs #21443.

Backport of 4fcc1e4ad8d153f41132b171c231b6d5d4086c28 from master.
[1.5.x] Fixed #21702 -- Added different bullet styles for nested lists.

Thanks moc at mocpa.com for the suggestion.

Backport of c81b6f7b83 from master
[1.5.x] Fixed #21120 -- Added more explicit text on using validators and link to writing validators.

Thanks nicolas at niconomicon.net for the suggestion.

Backport of 98e0453f00 from master
[1.5.x] Fixed #20830 -- Clarified that Django uses a customized version of six.

Thanks glarrain for the suggestion.

Backport of a53caf28bf from master
[1.5.x] Removed implication that six is part of Python stdlib.

Backport of 45969bdeb5 from master
[1.5.x] Removed extra p (topppings->toppings)

Backport of 946a2226ea from master
[1.5.x] Fixed #21137 -- Corrected ULRconf include example.

Thanks marfire for the report.

Backport of 77f6b468e5 from master
Revert "[1.5.x] Ensure that passwords are never long enough for a DoS."

This reverts commit 22b74fa09d7ccbc8c52270d648a0da7f3f0fa2bc.

This fix is no longer necessary, our pbkdf2 (see next commit) implementation
no longer rehashes the password every iteration.
[1.5.x] Fixed #21138 -- Increased the performance of our PBKDF2 implementation.

Thanks go to Michael Gebetsroither for pointing out this issue and help on
the patch.

Backport of 68540fe4df44492571bc610a0a043d3d02b3d320 from master.
[1.5.X] Fixed wording in unit tests documentation.

Backport of 42b9feb2e79546e1d4362c3a4f0043f3c569ace3 from master.
[1.5.x] Fixed #21126 -- QuerySet value conversion failure

A .annotate().select_related() query resulted in misaligned rows vs
columns for compiler.resolve_columns() method.

Report & patch by Michael Manfre.

Backpatch of 83554b018ef283827c0e7459ab934d447b3419d5 from master.