Bug#701769: new location for wheezy-backports
the wheezy-backports is no longer located in backports.debian.org. It is
now included on ftp.*.debian.org (it's already there).
I think it would be good to mention this in the release notes. Maybe
section 4.2.5 ("Unofficial sources and backports") would be a good
place? It suggests to look if additional archives such as backports also
provide packages for wheezy and update the sources.list entry