Backport of e2b77ace from master

Avoided split_exclude() for Q when used as an expression.

Backport of bc87061a from master

Backport of 8b106cfa from master

Backport of fb94e7b8 from master

Backport of f3b51f51 from master

Refs #24503.
Backport of 1046c8af from master.

Backport of a0175724 from master

Backport of f5da4380 from master

Backport of e4f0e5a9 from master

Thanks Markus Holtermann for review.

Backport of 307acc74 from master

Backport of fc1eea59 from master

Thanks Carl Meyer and Tim Graham for the reviews.
Backport of 32260503 from master.

Backport of 2dee853e from master

Thanks Thomas Recouvreux for the report and Tim Graham for the tests and
review.
Backport of ae635cc3 from master.

Backport of a37dcfd0 from master

Backport of dce004ab from master

Backport of 3c8fe5dd from master

Backport of 81d4ce4a from master

Backport of ca51c559 from master

Arguments shown in example code (signal, sender, instance) appeared to
be the incorrect positional arguments for a post_save signal (which
might start as: sender, instance, created), as documented:
​https://docs.djangoproject.com/en/1.8/ref/signals/#post-save

Backport of 4f3c4442 from master.

Fixed crashes with ForeignKey to UUIDField and inheritance with UUIDField
primary keys.

Backport of ec74dba2 from master

When the query's model had a self-referential foreign key, the
compiler.get_group_by() code incorrectly used the self-referential
foreign key's column (for example parent_id) as GROUP BY clause
when it should have used the model's primary key column (id).

Backport of adc57632 from master

Backport of be9d6453 from master

Backport of 8e86d9d3 from master

Backport of c21b832c from master

Backport of b99114f6 from master

Backport of 1a62f197 from master

Backport of 756a7272 from master

Backport of 3baebf52 from master

Backport of 783572ab from master

Backport of 64ed8cdc from master

Case expressions weren't copied deep enough (self.cases list was
reused resulting in an error).

Backport of 7b05d2fd from master

Backport of 9096e2b5 from master

The inner import was dropped during the reorganizing of the database
backends in commit 28308078.

Backport of 95058606 from master

Backport of 17b1f788 from master

Backport of 81f76517 from master

Thanks Preston Timmons for the report.

Backport of 1563b897 from master

Backport of b0bd1f0e from master

Backport of 3cb386b8 from master