Fixed small typo in django-admin.txt

The word 'by' seemed to be missing from the first line of the compilemessages command.
Noted that pip is included with Python 3.4 in Windows install guide.

Thanks CHI Cheng.
Used more specific test assertions.
Fixed #21553 -- Ensured unusable database connections get closed.
Fixed #22401 -- Deprecated regular expression parsing of initial SQL in favor of installing sqlparse.
Fixed #22343 -- Disallowed select_for_update in autocommit mode

The ticket was originally about two failing tests, which are
fixed by putting their queries in transactions.

Thanks Tim Graham for the report, Aymeric Augustin for the fix,
and Simon Charette, Tim Graham & Loïc Bistuer for review.
Documentation fixes for the select_for_update change.

Refs #22343; thanks Tim Graham for the fixes.