Moved ServerHandler helper class to tests.

It has been only used in the builtin_servers tests since Django 1.4.
Fixed #14226 -- Dependency calculation for complex M2M relations.

`sort_dependencies` incorrectly interpreted 'complex' M2M relations
(with explicit through models) as dependencies for a model. This caused
circular complex M2M relations to be unserializable by dumpdata.

Thanks to aneil for the report and outofculture for initial tests.
Unneeded, Python 3 incompatible code in a75324c6 tests.
Fixed #20936 -- When logging out/ending a session, don't create a new, empty session.

Previously, when logging out, the existing session was overwritten by a
new sessionid instead of deleting the session altogether.

This behavior added overhead by creating a new session record in
whichever backend was in use: db, cache, etc.

This extra session is unnecessary at the time since no session data is
meant to be preserved when explicitly logging out.
Fixed some test models' natural_key() methods.
Completed long overdue sqlinitialdata deprecation.
Fixed #22613 -- Added formfield_for_choice_field() to the list of methods that InlineModelAdmin supports.
Fixed flake8 error.
Added 1.6.5 release note for refs #22508.
Fixed #22619 -- Corrected description of os.path.

Thanks Collin Anderson for the report.
Fixed #22618 -- Improved import_string example.

Thanks ewjoachim for the sugggestion.
Removed some references to django.contrib.comments which has been removed.
Fixed typo in transactions.txt
Fixed #22533 -- Added label_suffix parameter to form fields.

Fields can now receive the `label_suffix` attribute, which will override
a form's `label_suffix`.

This enhances the possibility to customize form's `label_suffix`, allowing
to use such customizations while using shortcuts such as
`{{ form.as_p }}`.

Note that the field's own customization can be overridden at runtime by
using the `label_prefix` parameter to `BoundField.label_tag()`.

Refs #18134.
Fixed spelling mistake and added a word to the word list.
Removed an unnecessary anchor in the docs.
Dropped fix_IE_for_vary/attach.

This is a security fix. Disclosure following shortly.
Added additional checks in is_safe_url to account for flexible parsing.

This is a security fix. Disclosure following shortly.
Added release notes for 1.4.13, 1.5.8, 1.6.5.
typo: urlaprse -> urlparse