[1.6.x] Documentation -- Improved description of cache arguments

- Fixed some grammar and formatting mistakes
- Added the type and default for CULL_FREQUENCY
- Made the note on culling the entire cache more precise. (It's actually
  slower on the filesystem backend.)

Backport of 5eca021d48 from master
[1.6.x] Fixed #20887 -- Added a warning to GzipMiddleware in light of BREACH.

Thanks EvilDMP for the report and Russell Keith-Magee
for the draft text.

Backport of da843e7dba from master
[1.6.x] Minor typo fix in django.contrib.auth.models.User docs

Backport of bd72c2acb6 from master
[1.6.x] Fixed a couple of typos in GeoDjango docs.

8b366a50f4 from master.
[1.6.x] Fixed #21095 -- Documented new requirement for dates lookups.

Day, month, and week_day lookups now require time zone definitions in the database.

Backport of 9451d8d from master.
[1.6.x] Documentation -- added instructions on working with pull requests

Since non-core contributors are asked to review patches, instructions
on working with pull requests were added to the Working with Git and
GitHub page (based on the existing instructions in the core
committers page).

Backport of 990ce9aab9 from master
[1.6.x] Fixed #21094 -- Updated reuseable apps tutorial to use pip for installation.

Thanks ylb415 at gmail.com for the suggestion.

Backport of e4aab1bb8d from master
[1.6.x] Fixed #21100 -- Noted that Create/UpdateViews.fields is new in 1.6

Thanks AndrewIngram for the suggestion.

Backport of ec89e1725a from master
[1.6.x] Fixed #21101 -- Updated urlize documentation to mention email addresses

Backport of 39b49fd339 from master
[1.6.x] Added tests for double-pickling a QuerySet

Refs #21102.

Backpatch of 74b91b3888383fca28dea00e0e1ffb5aecec7c0f
[1.6.x] Ensure that passwords are never long enough for a DoS.

 * Limit the password length to 4096 bytes
  * Password hashers will raise a ValueError
  * django.contrib.auth forms will fail validation
 * Document in release notes that this is a backwards incompatible change

Thanks to Josh Wright for the report, and Donald Stufft for the patch.

This is a security fix; disclosure to follow shortly.

Backport of aae5a96d5754ad34e48b7f673ef2411a3bbc1015 from master.
[1.6.x] Add release notes and bump version number for security release.
[1.6.x] Cleaned up 1.5.4/1.4.8 release notes

Backport of 8d29005524 from master
[1.6.x] Reworded a paragraph in the logging docs.

9d12f68a53 from master.
[1.6.x] Fixed #21109 -- made db cursor error wrapping faster

Backpatch of 94001421321bd8808c4027a72aa32a1eef005764 from master.
[1.6.x] Final attempt to solve sporadic test failures.

tearDownClass is not called if setUpClass throws an exception, in our case
this means that LiveServerTestCase leaks LiveServerThread sockets if the
test happens to be skipped later on, and AdminSeleniumWebDriverTestCase
doesn't close it's already open browser window. To prevent this leakage
we catch errors where needed and manually call _tearDownClassInternal.
_tearDownClassInternal should be written as defensively as possible since
it is not allowed to make any assumptions on how far setUpClass got.

This patch should fix the sporadic "Address already in use"-errors on jenkins
and also the "This code isn't under transaction management"-error for sqlite
(also just on jenkins).

After discussion with koniiiik, jezdez, kmtracey, tos9, lifeless, nedbat and
voidspace it was decided that this is the safest approach (thanks to everyone
for their comments and help). Manually calling tearDownClass was shut down
cause we don't know how our users override our classes.

This is a private and very specialized API on purpose and should not be used
without a strong reason!

This patch partially reverts the earlier attempts to fix those issues,
namely:
	2fa0dd73b18f55d0fdd1c1d54b1d18031bfcf1ed and
	3c5775d36f7e431d9691829a78580873111cb714

Final note: If this patch breaks in a later version of Django, please be
very careful on how you fix it, you might not see test failures locally.
That said, this patch hopefully doesn't produce even more failures.

Backport of 73a610d2a81bc3bf2d3834786b2458bc85953ed0 from master.
[1.6.x] Fixed #15625 -- Made message in MultiValueDictKeyError less verbose.

Thanks margieroginski for the suggestion.

Backport of 893198509e from master
[1.6.x] Fixed #21118 -- Isolated a test that uses the database.

Thanks rmboggs for the report.

Backport of 4f40b97d97 from master
[1.6.x] Fixed bad backport in last commit; refs #21118
[1.6.x] Fixed #21098 -- Applied sensitive_post_parameters to MultiValueDict

Thanks simonpercivall for the report and bmispelon for the review.

Backport of 2daada800f from master