While Node class has a useful `__str__`, its `__repr__` is not that
useful. Added a `__repr__` that makes use of the current `__str__`.
This is especially useful since the more popular `Q` class inherits
`tree.Node`. Also created new tests that cover most of `Node` class
functionality.

It was previously used in a test that was deprecated and then removed, this cruft can be removed now.

Thanks to Claude Paroz for the report and patch and Tomasz
Paczkowski for the review.

Forwardport of 79f15ab1 from stable/1.7.x

cater for running tests from another directory than tests

cater for running tests from another directory than tests - applying existing pattern to newly added test_testcase_ordering as well

Thanks nikolay.v.golub@gmail.com for the report.

Added DateTimeCheckMixin to avoid the use of default, auto_now, and
auto_now_add options together. Added the fields.E151 Error that is raised
if one or more of these options are used together.

In django.db.backends.BaseDatabaseWrapper, pulled the creation of
cursors in the non-debug case into a separate method, in order to
make behavior more consistent when overriding the cursor creation
in derived classes.

Thanks Stephen Burrows for work on the patch as well.

Forwardport of 2914f669 from stable/1.7.x

Fix typo that disabled code example highlighting

typo: urlaprse -> urlparse

This is a security fix. Disclosure following shortly.

This is a security fix. Disclosure following shortly.

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.

Thanks ewjoachim for the sugggestion.

Thanks Collin Anderson for the report.

Fixed #22613 -- Added formfield_for_choice_field() to the list of methods that InlineModelAdmin supports.

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.

`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.