Backport of dda2a3cf from master

These cached properies were causing problems with pickling, and in
addition they were confusingly defined: field.rel.model._meta was
not the same as field.rel.opts.

Instead users should use field.rel.related_model._meta inplace of
field.rel.opts, and field.rel.to._meta in place of field.rel.to_opts.

Backport of f95122e5 from master

Switched from an adjancency list and uncached, iterative depth-first
search to a Node-based design with direct parent/child links and a
cached, recursive depth-first search. With this change, calculating
a migration plan for a large graph takes several seconds instead of
several hours.

Marked test `migrations.test_graph.GraphTests.test_dfs` as an expected
failure due to reaching the maximum recursion depth.

Backport of 78d43a5e from master

Backport of 7fa7dd48 from master

Refs #24389.

Backport of 556a7487 from master

Backport of b2f331dc from master

Backport of ff5e47e7 from master

Backport of 7901eccf from master

Thanks uranusjr for the report and analysis.

Backport of 88a5f17d from master

Backport of eba6dff5 from master

Backport of ea3168dc from master

Backport of 787dd651 from master

In addition to simplifying the code, this reduces the number of writes.

Backport of bd059e3f from master

This makes the staticfiles tests 2.5 times faster.

Backport of 2bb5b0e0 from master

Backport of bd059e3f from master

It should have been removed when the ADMIN_MEDIA_PREFIX setting was deprecated.

Backport of 1d9d39fa from master

Refs 5355baf6.

This reverts commit 88e6fbb2.

Backport of 99a1bbf9 from master

Backport of 1d1d5d1c from master

Explicit is better than implicit.

Backport of 51b606f7 from master

Backport of bad5f262 from master

The new signature enables better support for routing RunPython and
RunSQL operations, especially w.r.t. reusable and third-party apps.

This commit also takes advantage of the deprecation cycle for the old
signature to remove the backward incompatibility introduced in #22583;
RunPython and RunSQL won't call allow_migrate() when when the router
has the old signature.

Thanks Aymeric Augustin and Tim Graham for helping shape up the patch.

Refs 22583.

Conflicts:
	django/db/utils.py

Backport of bed504d7 from master

Backport of 1f9e4403 from master

Backport of dd0b4878 from master

Thanks to DavidMuller for the report.

Backport of c490e410 from master

As suggested by Anssi. This has the slightly strange side effect of
passing the expression to Expression.convert_value has the expression
passed back to it, but it allows more complex patterns of expressions.

Backport of 32d4db66 from master

Joint effort between myself, Josh, Anssi and Shai.

Conflicts:
	django/db/models/query.py
	tests/model_fields/models.py

Backport of 4755f8fc from master.

Backport of e467919c from master

This opens more possibilities, like accessing context.template.origin.

It also follows the chain of objects instead of following a shortcut.

Backport of 1bfcc950 from master

Workaround for http://bugs.python.org/issue20747.
In some corner cases, Python 2 inserts a newline in a header value
despite `maxlinelen` passed in Header constructor.
Thanks Tim Graham for the review.
Backport of efb1f99f from master.

Thanks Joris Benschop for the report, and Tim Graham for the tests.

Backport of ceadc94f from master

Thanks Tim Graham for pointing out the fix.

Backport of f7d34fe7 from master ticket_24362

Swapped out models don't have a _default_manager unless they have
explicitly defined managers. ModelState.from_model() now accounts for
this case and uses an empty list for managers if no explicit managers
are defined and a model is swapped out.

Backport of 15dc8d1c from master

Backport of e9282747 from master

Backport of b8d6cdbc from master

If Django is installed in a path that contains non-ASCII characters,
the tag failed with UnicodeDecodeError.

Backport of 098fa12d from master

[1.8.x] Refs #24324 -- Fixed Python 2 test failures when path to Django source contains non-ASCII characters.

Backport of 307c0f29 from master

Backport of fa66ea75 from master