Fixed #25672 -- Clarified why related ManyToManyFields with a custom intermediate model disable the remove() method.

Due to randomness of garbage collection with geometry objects, it's
easier to simply ignore AttributeError/TypeError generally raised when
parts of objects are already garbage-collected.
Thanks Sergey Fedoseev and Tim Graham for reviewing the patch.

URLValidator now validates the maximum length of a hostname and the
maximum length of all labels inside the hostname.

Thanks Justin Abrahms for the report.

Thanks Jonas Haag for report and review.

Thanks to Jean Gourds for the report, Tim and Claude for the review.

This allows setting a Content-Security-Policy HTTP header
(refs #15727).

Special thanks to blighj, the original author of this patch.

This also fixes a possible data eviction race condition between
setting and getting a key. Another thread could remove the key
before get_and_set() accesses it again. In this case, now the
default value will be returned instead of None.

Some versions of GDAL give slightly different results.

This is useful for certain language translations.

This skips some tests on systems with GEOS < 3.3 (the minimum
supported version).

When Django reraises an exception, it sets the __cause__ attribute even
in Python 2, mimicking Python's 3 behavior for "raise Foo from Bar".
However, Python 3 also ensures that all exceptions have a __traceback__
attribute and thus the "traceback2" Python 2 module (backport of Python
3's "traceback" module) relies on the fact that whenever you have a
__cause__ attribute, the recorded exception also has a __traceback__
attribute.

This is breaking testtools which is using traceback2 (see
https://github.com/testing-cabal/testtools/issues/162).

This commit fixes this inconsistency by ensuring that Django sets
the __traceback__ attribute on any exception stored in a __cause__
attribute of a reraised exception.

Complements 7127eb28.

xato.net is dead; replaced with link to archive.org.