Fixed #22838 -- Deprecated ModelChoiceField.cache_choices.

Undocumented, untested and probably not even useful feature.
Fixed test from refs #22782.
Added refs #22514 to 1.6.6 release notes.
Prevented evaluation of a possible lazy message

As far as possible, message evaluation should not happen in field
__init__ (often run at import time).
Fixed #22793 -- Updated import location for GeometryColumns in tests

The old location was removed in cebd8753c6.
Thanks Aymeric Augustin for the report.
Removed some apps from ALWAYS_INSTALLED_APPS
Fixed #22867 -- Memoized django.utils.version.get_git_changeset().

This follows commits 80f4487 and 01399fa; original patch had to be
reverted because it wasn't Python 2.6 compatible and we need it to
be in order to build docs on the djangoproject.com server.

This fix should be replaced by @lru_cache as soon as we drop
Python 2.6 compatibility.

Thanks Florian Apolloner for the review and Alexander Schepanovski
for the original patch.
Fixed #22875: Optimizer did not take through= into account.
Include swapped apps in autodetector state
Clean up syncdb parts of migrate output if no synced apps
Fixed #22881 -- Better soft_applied migration detection
Fixed #8033 -- Explained app registry error during translation setup

Thanks Tim Graham and Aymeric Augustin for the review.
Cleaned temp dir in symlinks_supported()

Refs #21482.
Ensured cache tests do not leak temp dirs

Refs #17215.
Created import-time test temp dirs in known location

Refs #17215. In the same spirit as 5de31cb8cb.
Fixed #22888 -- Removed some unnecessary text in tutorial 3.
Fixed test failures introduced by refs #22881.
Refactored common code in handlers/base.py and urlresolvers.py