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
Fixed #19402 - Clarified purpose of CustomUser.REQUIRED_FIELDS

Thanks pydanny for the report and ptone for the patch.
Merge pull request #804 from oinopion/ticket18162

Fixes #18162 --  Specifying choices to Field overrides any form_class argument
Fixed #19282 -- Restored ability to pass Decimals to intcomma filter
Added an example of "default" database dictionary left blank; refs #19775.

Thanks wsmith323 for the patch.
Some style fixes for stuff that was clearly brough tover from doctests.
Fixed #18829 -- Fixed ModelChoiceIterator length

Thanks facundo.olano at gmail.com for the report and thikonom for
the initial patch.
Fixed #19526

CSS specifications governs that syntax is case insensitive.
This modifies CachedFilesMixin to support that.
Merge pull request #809 from asendecka/ticket19526

Fixed #19526 - make regexes for css case insensitive
Fixed #19872

Made cached_property to behave as property when accessed via class.
Fixed #18491 -- deleting a proxy doesn't show warning about cascade deletes
Merge branch 'ticket19872' of https://github.com/oinopion/django
Merge pull request #778 from viciu/19609

Fixed #19609: admin Inlines doesn't display help_text for readonly fields
fixes #19263
Merge pull request #813 from HiddenData/ticket-19263

fixes #19263 - EmptyResultSet in subquery causes incorrect SQL
Sorry, accidental commit, Thanks claudep for catching it!