Fixed #22302 -- Updated Finnish locale formats
Improved strip_tags and clarified documentation

The fact that strip_tags cannot guarantee to really strip all
non-safe HTML content was not clear enough. Also see:
https://www.djangoproject.com/weblog/2014/mar/22/strip-tags-advisory/
Avoided transactional DDL on castrated databases.

Fixed a test failure that appeared after 753a22a6, although the bug
existed before that commit.

Refs #22308.
Added release note about strip_tags improvement
Made ModelForm, modelform_factory, modelformset_factory, and generic model views raise ImproperlyConfigured if the list of fields is not explicitly specified.

refs #19733.