This enables using a custom user model with a primary key with a name
different than 'id'; refs #22889.

Refs #17215. In the same spirit as 5de31cb8.

Refs #17215.

Refs #21482.

Thanks Tim Graham and Aymeric Augustin for the review.

This follows commits 80f4487d and 01399fa0; 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.

The old location was removed in cebd8753.
Thanks Aymeric Augustin for the report.

As far as possible, message evaluation should not happen in field
__init__ (often run at import time).

Undocumented, untested and probably not even useful feature.

It makes possible to have your sitemap in multiple languages when
using i18n in URLs.

Thanks Ian Foote.

Thanks artortenburger for the report.

Thanks Russell Keith-Magee and Tim Graham for reviews.

This reverts commit 80f4487d temporarily, because that commit prevented
the djangoproject.com server from building the docs, because it still
uses Python 2.6.

This improves pickling speed in prelease versions of Django; refs #21430.

Thanks flisky for the report.

Thanks jorgecarleitao and mmardini for reviews.

Thanks to jonathanmorgan for the report and initial patch.

Thanks to Chris Beaven.