Thanks Rémy Hubscher, Ramiro Morales, Unai Zalakain and
Tim Graham for the reviews.
Also fixes #16084.

Refs #20199 #16986.

Thanks @akaariai, @bmispelon, @mjtamlyn, @timgraham for the reviews.

Previously when collecting static files, the directories would receive permissions
from the global umask. Now the default permission comes from FILE_UPLOAD_DIRECTORY_PERMISSIONS
and there's an option to specify the permissions by subclassing any of the
static files storage classes and setting the directory_permissions_mode parameter.

Use 'update_fields' in RelatedManager.clear() when bulk=False.

Thanks Simon Charette for the suggestion.

Refs #21169.

Thanks Rhett Garber for the report and initial patch.

Thanks to trac user oubiga for the report.

Thanks Preston Holmes for the draft text.

Fixed typo in release notes.

Refs #21169

Refs #21169

Refs #21169

The `remove()` and `clear()` methods of the related managers created by
`ForeignKey`, `GenericForeignKey`, and `ManyToManyField` suffered from a
number of issues. Some operations ran multiple data modifying queries without
wrapping them in a transaction, and some operations didn't respect default
filtering when it was present (i.e. when the default manager on the related
model implemented a custom `get_queryset()`).

Fixing the issues introduced some backward incompatible changes:

- The implementation of `remove()` for `ForeignKey` related managers changed
  from a series of `Model.save()` calls to a single `QuerySet.update()` call.
  The change means that `pre_save` and `post_save` signals aren't called anymore.

- The `remove()` and `clear()` methods for `GenericForeignKey` related
  managers now perform bulk delete so `Model.delete()` isn't called anymore.

- The `remove()` and `clear()` methods for `ManyToManyField` related
  managers perform nested queries when filtering is involved, which may
  or may not be an issue depending on the database and the data itself.

Refs. #3871, #21174.

Thanks Anssi Kääriäinen and Tim Graham for the reviews.

Application template now includes an empty migrations module, and
the autodetector will only make initial migrations for apps with
empty modules.

Fixed #21499 -- Migrations won't work if field signature changes

Thanks Gunnar Scherf for the report and the suggested patch.

Fixed #21512 -- Added more complete information about Pillow and PIL in model_fields and model_forms tests.

Updated ModelAdmin to use form.instance when passing parent model to
child inlines for add_view. There is effectively no change in the
change_view since the previously passed 'obj' is the same as form.instance.

Thanks to meshy for report, and EvilDMP and timo for review.

Since Python 2.5, KeyboardInterrupt and SystemExit are not subclasses of
Exception, so explicitly reraising them before the “except Exception” clause
is not necessary anymore.