NullHandler removed in 1.9; unused since Django 1.5.

Setting a cookie with the same name as a previously deleted cookie
would set its expiry date to 'Thu, 01-Jan-1970 00:00:00 GMT'.

Thanks Graham Wideman for the patch.

Thanks Graham Wideman for the patch.

Forward port of 5234c993 from stable/1.9.x

Avoided unnecessary list operations and delattr() calls that result
in an exception being raised as it causes call frame reconstruction
which is very costly, especially so in a function that is called
millions of times.

The original intent in refs #20536 was to use the highest protocol.
Calling zlib.compress() with a compression level of -1 seems to
fall back to the default level of 6.

Thanks Fako Berkers for help with the patch.

This reverts commit 49eee842 as it caused
a regression with test mirrors.