Fix pep8 violation in migration template.
Fixed #21952 -- signals deadlock due to locking + weakref interaction
Simplified signal code.

Refs #21952
Fixed gendered examples in the docs.
Fixed ImportError when running contrib.gis tests without libgeos installed.
Revert "Fixed #20296 -- Allowed SafeData and EscapeData to be lazy"

This reverts commit 2ee447fb5f8974b432d3dd421af9a242215aea44.

That commit introduced a regression (#21882) and didn't really
do what it was supposed to: while it did delay the evaluation
of lazy objects passed to mark_safe(), they weren't actually
marked as such so they could end up being escaped twice.

Refs #21882.
Added previous commit to 1.6.2 release notes.
Removed import which is now unused
Extended the release notes for chainable Manager/QuerySet methods.

Refs #20625.
Added missing items to 1.6.2 release notes.