Fixed #19945 -- Fixed default User model Meta inheritance.

Updated default User model Meta class to extend AbstractUser Meta
where translated verbose_name and verbose_name_plural are
defined.
Removed unnecessary imports.
Fix Typo explicitly. Fixes #19971
Fixed #19942 -- Decoded errors coming from Popen commands

Thanks Aymeric Augustin for reporting the issue.
Merge pull request #877 from tcarlander/master

Fixed #19971 -- Typo in CBV docs.
Fixed #19915 - Made blocktrans tag honor TEMPLATE_STRING_IF_INVALID.

Thanks Natalia Bidart for the report and Matías Bordese for the fix.
Release notes blurb for 804366327d728d23a9f7a25ff77a6eed3c9f9323.
Removed mentions of regressiontests.
Removed mentions of modeltests.
Merge pull request #871 from matiasb/ticket_19945

Fixed #19945 -- Fixed default User model Meta inheritance.
Fixed #19464 -- Eased customization of ClearableFileInput's link markup

Thanks rubyruy for the report and the patch.
Fixed #19838 -- Admin: Don't leak a 500 HTTP status when trying to delete protected FKs.

Thanks rafadev for the report and Javier Mansilla for the fix.
Fixed #6585 -- Admin relationship widgets: Respect ordering defined by target model's ModelAdmin.

Thanks Gary Wilson for the report and Juan Pedro Fisanotti, Carlos
Matías de la Torre for the fix.
Fixed minor warnings in tests.
Fixed #19989 -- Suppressed UnicodeWarning during BinaryField validation

Thanks Aymeric Augustin for the report and Simon Charette for the
review.
Fixed #19994 -- Typo.

Thanks akshar for the report.
Used more precise test assertions.
One more EMPTY_VALUES replacement following 22be90dd17

Thanks Loic Bistuer for catching this omission. Refs #19989.
Update link to django-mssql project
Merge pull request #884 from manfre/patch-1

Fixed #19996 - Updated link to django-mssql project in docs.