This change allows dynamically created inlines "Add related" button to work
correcly as long as their associated foreign key is pointing to the primary
key of the related model.

Thanks to amorce for the report, Julien Phalip for the initial patch,
and Collin Anderson for the review.

Thanks Redouane Zait for the report.

Previous algo only worked if the first item was a part of the loop,
and you would get an infinite loop otherwise (see test).

To fix this, it was much easier to do a pre-pass.

A bonus is that you now get an error message that actually helps you debug
the dependency problem.

When the test client detects a redirect to a URL seen in the
currently followed chain it will now raise a RedirectCycleError
instead of just returning the first repeated response.

It will also complain when a single chain of redirects is longer
than 20, as this often means a redirect loop with varying URLs,
and even if it's not actually one, such long chains are likely
to be treated as loops by browsers.

Thanks Preston Timmons, Berker Peksag, and Tim Graham for reviews.

These assertions had been removed in 34ba8670 and 7fe554b2,
seemingly because they were referencing the wrong objects, and so
they started failing when the checking of object types (as well as
PK values) was introduced.

This is useful for debugging side effects affecting tests that
are usually executed before a given test. Full suite and pair
tests sort cases more or less deterministically, thus some test
cross-dependencies are easier to reveal by reversing the order.

Thanks Preston Timmons for the review.

The Jython bug was fixed in http://bugs.jython.org/issue1518
(tested on Jython 2.7b3); also updated make_msgid() to be more like
the version in Python 3.2+; refs #23905.

Thanks Simon Charette for testing and review.

- commit/rollback are no longer replaced by nop
- the warning about not using TestCase when testing transactional
  behavior belongs to TestCase section, not TransactionTestCase

This rename is very tricky for the case of subclasses which define
get_query_set and haven't been updated yet, which applies to all projects in
the form of RelatedManager from Django 1.5.

Thanks Luke Plant for the report.

This way they won't need to fix things again when get_query_set disappears

The Preventing header injection example included
classes that are not imported.

Thanks to Collin Anderson and Berker Peksağ for the
reviews.

Since RequestContext doesn't know its Engine until it's passed to
Template.render() -- and cannot without breaking a widely used public
API -- an elaborate hack is required to apply context processors.

It's only available during the rendering.

Passed the engine instance to loaders. This is a prerequisite for
looking up configuration on the engine instance instead of global
settings.

This is backwards incompatible for custom template loaders that override
__init__. However the documentation doesn't talk about __init__ and the
way to pass arguments to custom template loaders isn't specified. I'm
considering it a private API.

It was introduced in a recent refactoring so this isn't an issue.

Then renamed _get_template_loaders to get_template_loaders.