[1.7.x] Fixed typo in docs/ref/checks.txt.

Backport of 2ca244aae6 from master
[1.7.x] Fixed imports in `Sitemap for static views` example

Backport of 344f37718b from master
[1.7.x] Added missing periods in docs/ref/checks.txt.

Backport of 5d04433903 from master
[1.7.x] Fixed typo in docs/topics/checks.txt.

Backport of 0f90f741de from master
[1.7.x] cater for running tests from another directory than tests - applying existing pattern to newly added test_testcase_ordering as well

Backport of d11e836203 from master
[1.7.x] Fixed #22534: Reinforce swappable documentation
[1.7.x] Fixed #22411: Throw a more helpful error if contenttypes doesn't exist.

Conflicts:
	django/contrib/contenttypes/models.py
[1.7.x] Fixed #23414 -- Updated version numbers in release process doc.

Thanks jaap3 for the report.

Backport of 5c5011ce68 from master
[1.7.x] Update docs to be more clear about nested classes (refs #23418)
[1.7.x] switch out recursive dfs for stack based approach, to avoid possibly hitting the recursion limit
[1.7.x] Fix Python 3 incompatability
[1.7.x] Fixed #23427 -- Documented migrate is required before runserver for default projects.

Backport of fb545e5a27 from master
[1.7.x] Fixed #23430 -- simplified gunicorn deployment docs.

Backport of 77b3907d6d from master
[1.7.x] Fixed #22161 -- Documented send() with no recipients won't raise an exception.

Backport of 0f0a5c07f9 from master
[1.7.x] Fixed #23438 -- Added snippet & imports to docs/intro/overview.txt.

Backport of 88c4e01d34 from master
[1.7.x] Fixed #23340 -- Corrected naturaltime docs to match behavior.

Thanks zachborboa for the report and blackguest for the patch.

Backport of 7353e26d5d and 0a2bc6e6bd from master
[1.7.x] Fixed #22882 -- Fixed a UnicodeDecodeError in flush.

Thanks djbaldey for the report.

Backport of 0e4d79c4f0 from master
[1.7.x] Refs #23430 -- gunicorn wants a module, not file

Backport of fa74dba994 from master
[1.7.x] Fixed #23437 -- Documented required update of WSGI scripts for 1.7.

Thanks Tim for the review.

Backport of dfe209a from master
[1.7.x] Fixed #23416 -- Make sure DatabaseCreation respects checks.

Migrations respected Field.db_parameters()['check'], but
DatabaseCreation was still using just Field.db_type().

Backport of 14c8456 from master