Comment 2 for bug 549041

Short version: for distro series >> lucid, please only remove source
packages from indices files when they're actually due to be removed
from disk.

Long version: So, on reflection, there is actually a soyuz bug here.
I can fix our magic mirror script for the archive / ports use case.
However a third use case for (the/a) magic mirror script is
old-releases. With source in the archive but not in the indices
files, it's extremely non-trivial to (in an automated fashion) get a
GPL compliant mirror of any given distro-series.

I think we should fix this by no longer automatically removing source
packages from indices files when there's a newer version, but instead
only removing them from indices files when the source packages are
about to be removed from disk.

This does mean that any given Sources file could have several versions
of any given source package which may break some tools that are not
expecting this. However the Debian folks have apparently being
publishing multiple versions of a given source package in Sources
files for a couple of months now, so presumably tools will started to
get fixed.