[1.7.x] Clarified that makemessages -l takes a locale name, not a language code.

Backport of 5473c36cef from master
[1.7.x] Fixed spelling mistake in file docs.

Backport of a3e88e64a4 from master
[1.7.x] Fixed #23362 -- Clarified "database columns as attributes" in tutorial.

Backport of 035f2e699c from master
[1.7.x] Fixed #17719 -- Documented that template syntax sequences cannot be used as string literals.

Backport of e02f45d5ea from master
[1.7.x] Fixed #19312 -- Documented MySQL TIMESTAMP columns cannot be used with USE_TZ=True.

Backport of 348c89cbfb from master
[1.7.x] Fixed #17707, #20734 -- Added examples to URL namespacing docs.

Thanks Daniele Procida for review.

Backport of a2bcec3491 from master
[1.7.x] Fixed #23250 -- Documented that ModelMultipleChoiceField queryset may be None.

Backport of ced3e303ca from master
[1.7.x] Fixed #21567 -- Documented how to deploy multiple sites using the sites framework.

Backport of 7b9537fb27 from master
[1.7.x] Fixed #22620 -- Emphasized role of DATABASE_ROTERS in multi-db docs.

Thanks Mike O'Connor for the suggestions.

Backport of 5ecead9ab9 from master