Fixed doc typos.
Fix keyword agument names in RunPython to be positional
Fixed #21948 -- Noted TEMPLATE_LOADERS requirement when overriding admin templates.

Thanks django at patjack.co.uk for the suggestion.
Removed some ReST links to undocumented functions.
Added release note and regression test for refs #21643.

This will be backported to stable/1.6.x along with the original fix.