Fixes #17866: Vary: Accept-Language header when language prefix used
Fixed #19775 - Clarified requirements of the "default" database.

Thanks monkut for the report and wsmith323 for the patch.
Fixed #19880 - Fixed an error in the form wizard initial_dict example.

Thanks almalki for the report.
Merge pull request #796 from ambv/vary

Fixes #17866: Vary: Accept-Language header when language prefix used
Fixed #19579 - Documented that "providing_args" is purely documentational.
Fixed 19895 -- Made second iteration over invalid queryset raise an exception too

When iteration over a queryset raised an exception, the result cache
remained initialized with an empty list, so subsequent iterations returned
an empty list instead of raising an exception