[1.6.x] Fixed #21510 -- Readded search reset link in changelist search bar

Thanks moritz.pfeiffer at alp-phone.ch for the report and
Tim Graham for the initial patch.
Backport of c7c647419c from master.
[1.6.x] Fixed #21473 -- Limited language preservation to logout

Current language is no longer saved to session by LocaleMiddleware
on  every response (the behavior introduced in #14825).
Instead language stored in session is reintroduced into new session
after logout.
[1.6.x] Added release note for #21473
[1.6.x] Added release note for #21358
[1.6.x] Added release note for #21443
[1.6.x] Additions and edits to the 1.6.1 release notes.
[1.6.x] Fixed #21594 -- Added note about model formsets deleting objects.

This behavior has been fixed in 65e03a424e. refs #10284.
Bumped version number for 1.6.1.
Merge tag '1.6.1' into fix-formset-deletion-1.6.x

Django 1.6.1

Conflicts:
	docs/topics/forms/modelforms.txt