add jessie preferences file
Merge branch 'master' of buse.riseup.net:shared-apt
add apticron_jessie symlink, same version in wheezy and sid
add apt listchanges template symlink for jessie - same as the others
Change default 50unattended-upgrades on Debian

* Use squeeze-lts origin on squeeze
* All other releases use newer Origins-Pattern format
* Drop support for lenny