"Area man/woman" is confusing to people not familiar with the
conventions of American journalism (like me).

Field.rel is now deprecated. Rel objects have now also remote_field
attribute. This means that self == self.remote_field.remote_field.

In addition, made the Rel objects a bit more like Field objects. Still,
marked ManyToManyFields as null=True.

Thanks Johannes Lerch for the report, Tim Graham for the test case,
and Simon Charette for the review.

This reverts commit da79ccca.

This optimized the unsuccessful case at the expense of the successful one.

Thanks Anssi Kääriäinen, Marc Tamlyn, and Tim Graham for the reviews.

Thanks to Russell Keith-Magee for mentoring this Google Summer of
Code 2014 project and everyone else who helped with the patch!

Thanks to github aliases dbrgn, carljm, slurms, dfunckt, and timgraham
for reviews.

Made _do_update behave more strictly according to its docs,
including a corner case when specific concurent updates are
executed and select_on_save is set.

Thanks Collin Anderson for the review.

This is a reliqua from the early days of the modeltests/regressiontests era.

Thanks Piotr Kasprzyk for help with the patch.

Signed-off-by: Jason Myers <jason@jasonamyers.com>

The option can be used to force pre 1.6 style SELECT on save behaviour.
This is needed in case the database returns zero updated rows even if
there is a matching row in the DB. One such case is PostgreSQL update
trigger that returns NULL.

Reviewed by Tim Graham.

Refs #16649

The __eq__ method now considers two instances without primary key value
equal only when they have same id(). The __hash__ method raises
TypeError for no primary key case.

Fixed #18864, fixed #18250

Thanks to Tim Graham for docs review.

Fixed #11892, fixed #16458, fixed #14492.

Should be unneeded with Python 2.7 and up.
Added some unicode_literals along the way.

Additionally this patch solves the orthogonal problem that specialized
`QuerySet` like `ValuesQuerySet` didn't inherit from the current `QuerySet`
type. This wasn't an issue until now because we didn't officially support
custom `QuerySet` but it became necessary with the introduction of this new
feature.

Thanks aaugustin, akaariai, carljm, charettes, mjtamlyn, shaib and timgraham
for the reviews.

Thanks Patryk Zawadzki.