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.

Forward port of 6a4649c2 from stable/1.9.x

Forward port of 3039d76b from stable/1.9.x

This was overlooked in 81f5d632.

Refs #25815. Thanks gunchleoc <fios@foramnagaidhlog.net> for the Scottish Gaelic
formats.py.

Refs #25815.

Thanks GunChleoc for the suggestions.

The check introduced in 4ce433e8 was too strict in real life. The poorly
implemented bots this patch attempted to ignore are sloppy when it comes
to http vs. https.

Thanks to Trac alias mrgaolei for the report, Baptiste for the confirmation
and Tim for the review.