[1.6.x] Fixed #21484 -- Documented that SQL logging does not include "framework level" queries.

Backport of 4d8d76e7a8 from master
[1.6.x] Fixed #21581 -- Fixed a number of issues with collectstatic.

When STATIC_ROOT wasn't set, collectstatic --clear would delete
every files within the current directory and its descendants.

This patch makes the following changes:

Prevent collectstatic from running if STATIC_ROOT isn't set.

Fixed an issue that prevented collectstatic from displaying the
destination directory.

Changed the warning header to notify when the command is run
in dry-run mode.

Backport of 4befb3015c from master
[1.6.x] Django sees more than 1mm hits per hour

Disqus regularly does 40-50k/s

Backport of a502bbb2f0 from master
[1.6.x] Fixed set literals for python 2.6
[1.6.x] Fixed minor typos.

Backport of 44d40ba521 from master
[1.6.x] Fixed typos. Changed grammar.

Backport of 6dd8631617 from master
[1.6.x] Fixed #21722 -- Added a warning for avoiding XSS vulnerabilities when reusing built-in filters.

Thanks Stephen McDonald for the suggestion.

Backport of 07711e9997 from master
[1.6.x] Fixed #21319 -- Added documentation for the Form.fields attribute.

Thanks pydanny for the report. Also, added documentation about
base_fields attribute and its difference with fields attribute.

Backport of ea83102d0f from master
[1.6.x] Fixed #21728 -- Corrected an inadvertent path change in docs/intro/contributing.txt.

Backport of e6800ea136 from master
[1.6.x] Fixed a sentence in the session security docs; thanks claudep.

Backport of 4d27d311f6 from master
[1.6.x] Fixed #21730 -- Removed superfluous db_index in custom auth docs

Thanks rafalp for the report.
Backport of c717ebbfec from master.
[1.6.x] Fixed typo in docstrings of MonthArchiveViews.

Backport of 270c9fe488 from master
[1.6.x] Fixed docstring typo in django/forms/forms.py.

Backport of 81bb8d1220 from master
[1.6.x] Fixed #21750 -- Fixed regression introduced by 4befb30.

Validating STATIC_ROOT in StaticFilesStorage.__init__ turned out to be
problematic - especially with tests - because the storage refuses to work even
if there are no actual interactions with the file system, which is backward
incompatible.

Originally the validation happened in the StaticFilesStorage.path method, but
that didn't work as expected because the call to FileSystemStorage.__init__
replaced the empty value by a valid path. The new approach is to move back the
check to the StaticFilesStorage.path method, but ensure that the location
attribute remains None after the call to super.

Refs #21581.

Backport of 1e9e7351f8 from master
[1.6.x] Fixed a test isolation issue. Refs #17062.

This test could change settings.DATABASES['default']['TIME_ZONE'] and
didn't restore the previous value.

Backport of 1c24096f from master.
[1.6.x] Fixed #21452 -- Non-autocommit connections to PostgreSQL.

When settings.DATABASES['default']['AUTOCOMMIT'] = False, the connection
wasn't in autocommit mode but Django pretended it was.

Thanks Anssi for analysing this issue.

Refs #17062.

Backport of 1afe7488 from master
[1.6.x] Fixed a test that was failing with PostGIS.

Fixed #21452 again.
[1.6.x] Fixed typo in storage docs

Backport of 82f466b571 from master
[1.6.x] Fixed #21747 -- Added {% elif %} to template topics guide.

Thanks gcc for the suggestion.

Backport of 9e5033b302 from master
[1.6.x] Fixed #21727 -- Added some links to help clarify topics/auth/default.txt

Thanks daGrevis for the suggestion.

Backport of d35f2bfd5b from master