Deprecate usage of boolean value for widget attributes

Django 1.7 will loudly warn when widget attributes are assigned
boolean values. In Django 1.8, False will mean attribute is not
present while True will mean attribute present without value.
Refs #20684.
Fixed 20613 - moved pickle loads/dumps outside with self._lock.reader()/writer() blocks
Additionaly added pickled=None initially and check for none before
returning in get
Tweaked proj string regex in gis tests
Added release dates for gis libs as doc comments
[gis] Dropped official support for GDAL < 1.6
Fixed #14006 -- Documented that Field's 'description' attribute is interpolated with field.__dict__

Thanks abeld for the suggestion.
Fixed #20711 -- Fixed broken link in timesince.py docstring
Removed some logic that wasn't needed following removal of some deprecated code.
.DS_Store can be ignored.
Merge branch 'ticket_20613' of https://github.com/ersran9/django into t20613
A few cleanups to capture the minimum amount of code in try/except blocks.
Fixed #13813 -- Comparison of DatabaseWrappers doesn't raise errors.

Patch from Lukasz Balcerzak.
Merge pull request #991 from stockr-labs/feature/email-backends-generators

Fixed #20194 -- Adds generators support for email backends that do not support it.
Replaced some dicts with sets.
Fixed a bug I introduced in my previosu ommit.
A large number of stylistic cleanups across django/db/
fixed a mis-importt in mysql/base.py
Use a more explicit check for whether these ids are None.
Clarified trac patch-related field meaning

There was some confusion on the mentorship list as to whether 'needs tests'
meant that a given ticket might not need tests, as opposed to flagging
a specific patch as still needing tests.

This commit seeks to clarify that confusion.
Merge branch 'docs-triage-needs-patch'