Fixed #21287 -- Fixed E123 pep8 warnings
Fixed bug causing CSRF token not to rotate on login.

Thanks Gavin McQuillan for the report.
Fixed ReST error in 1.6. release notes.
Added a warning regarding session security and subdomains.
Fixed #21212 -- Documented the reverse name for OneToOneField.

Thanks bjb at credil.org for the report.