Fixed #13518 -- Added FILE_UPLOAD_DIRECTORY_PERMISSIONS setting

This setting does for new directories what FILE_UPLOAD_PERMISSIONS
does for new files.

Thanks jacob@ for the suggestion.
Fixed #17778 -- Prevented class attributes on context from resolving as template variables.

Thanks KyleMac for the report, regebro for the patch, and Aymeric for the test.
Added missing release notes for older versions of Django
Unlocalize line numbers and ids in debug 500 view.

While using USE_L10N, line numbers and IDs were printed as comma (or
locale equivalent) separated values.

Thanks Kronuz for the report and intial patch.

Fixes #20861.
Fixed #20874 -- bump_prefix() in nested subqueries

Also made some cleanup to build_filter() code by introducing submethods
solve_lookup_type() and prepare_lookup_value().
Fixed overflow for the "Recent Actions" widget on the admin index.

Previously the CSS targeted "li.changelink" and therefore didn't
work for the "add" and "delete" actions.

Refs #14868.
Fixed #20883 -- Made model inheritance find parent links in abstract parents
Merge pull request #1470 from loic/admin.actionlist

Fixed overflow for the "Recent Actions" widget on the admin index.
Fixed test failure on MySQL

The fix for #20874 caused a MySQL specific failure.
Fixed is_safe_url() to reject URLs that use a scheme other than HTTP/S.

This is a security fix; disclosure to follow shortly.
Apply autoescaping to AdminURLFieldWidget.

This is a security fix; disclosure to follow shortly.
Added 1.4.6/1.5.2 release notes.
Fixed #20555 -- Make subwidget id attribute available

In `BoundField.__iter__`, the widget's id attribute is now passed to
each subwidget. A new id_for_label property was added to ChoiceInput.
Removed unneeded conditional_escapes from the testsuite.
Fixed #20864 -- Made the test client use common method for performing requests.
Fixed #11400 -- Passed kwargs from AbstractUser.email_user() to send_mail()

Thanks Jug_ for suggestion, john_scott for the initial patch,
and Tim Graham for code review.
Fixed #20709 -- Allowed {% widthratio %} to accept an "as" parameter.

Thanks clay.evil@ for the suggestion.
Added some doc links for django.contrib.messages