removed unused BLANK_CHOICE_NONE
Merge pull request #902 from evildmp/BLANK_CHOICE_NONE

Fixed #20043 -- Removed unused BLANK_CHOICE_NONE
Fixed #19635 -- Made fields pickleable
Fixed #19697 -- Added a deployment checklist.
Two additions to the deployment checklist.

Thanks Erik Romijn.
Minor docs fix for e11ccc76.
Fixed #19550 -- Made the filtered select widget wider in the admin.

Thanks Claude and Julien for the review.
Fixed #19510 -- Race condition in template loading.

Thanks Kronuz and regebro.
Fixed #17037 -- Added a --all option to diffsettings.
Clarified that constant_time_compare doesn't protect string lengths.
Fixed #18447 -- Made LazyObject unwrap on dict access.

Thanks Roman Gladkov and Zbigniew Siciarz.
Fixed #19456 -- Avoid infinite recursion when tracing LazyObject.__init__.

Thanks blaze33 for the patch.
Fixed #19968 -- Dropped support for PostgreSQL < 8.4.
Update versions and links to source tarballs.
Fixed #13260 -- Quoted arguments interpolated in URLs in reverse.
Added warn note to docs about MySQL issues with 0000-00-00 date strings

MySQL accepts 0000-00-00 as a valid date but MySQLdb converts those
values into None. So there will be problems for instance if trying to
transport the data using dumpdata/loaddata.

This patch refs #6642 that has been closed as wontfix since this is a
particular problem of MySQL.
Merge pull request #926 from catalanojuan/adds-dates-containing-zeros-note-to-docs

Added warn note to docs about MySQL issues with 0000-00-00 date strings
Fixed #19327 -- Added handling of double login attempts in admin.

Thanks to Krzysztof Jurewicz for initial patch and
adupin for tests.
small documentation update to outline caveat with SESSION_COOKIE_DOMAIN
Merge pull request #927 from ryanisnan/master

Documentation - Small update to SESSION_COOKIE_DOMAIN documentation