Comment 5 for bug 434243

Couple of notes:
- v=9.10 is not convenient to implement in livecd-rootfs as we only have the suite name; it would be possible to use n=karmic though; I don't think this would be updated across a dist-upgrade, so it seems sensible to have this support as generic as possible in livecd-rootfs and pin all series in the PPA equally
- o= is set to the Origin: field which is expected to be LP-PPA-$ppa with all slashes replaced with dashes; there's a catch though: PPAs named "ppa" have LP-PPA-foo as origin, not foo-ppa; this is for backward compatibility