[1.6.x] Fixed typo in docs/releases/1.4.9.txt.

Backport of 3b0293370a from master
[1.6.x] Fixed #21325 -- Added missing argument to permission_required decorator.

Backport of cc2049cdd7 from master
[1.6.x] Fixed #21335 -- Use importlib from python3 when using python3

Backport of 3351e94ffa from master.
[1.6.x] Removed relative usage of import_module

Python 3 version of importlib doesn't support this syntax.
Partial backport of fdd7a355bf. Refs #21335.