APT pinning for manual deb-multimedia.org usage

acolomb@multilus:/etc/apt$ cat preferences
Explanation: Only install package updates from deb-multimedia.org manually
Package: *
Pin: release l=Unofficial Multimedia Packages
Pin-Priority: 99

Explanation: Use the testing suite by default but avoid APT::Default-Release which would override the above rule
Package: *
Pin: release a=testing
Pin-Priority: 990

acolomb@multilus:/etc/apt$