Explanation: see http://www.argon.org/~roderick/apt-pinning.html
Package: *
Pin: release o=Debian,a=stable
Pin-Priority: 600

Package: *
Pin: release o=Debian,a=testing
Pin-Priority: 800

Package: *
Pin: release o=Debian,a=unstable
Pin-Priority: 300

Package: *
Pin: release o=jukie.net/amd64
Pin-Priority: 900

Package: *
Pin: release o=Debian
Pin-Priority: 1