[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.