Code review comment for lp:~julian-edwards/launchpad/no-udev-diff

= Summary =
Don't attempt diffs for the udev package, as they will currently fail and fill
the disk with output.

See https://bugs.edge.launchpad.net/soyuz/+bug/314436

= Implementation details =
Package diffs are requested in a single place,
ISourcePackageRelease.requestDiffTo(). They are created with a status of
PENDING and some time after the process-pending-diffs script runs and looks
for PENDING diffs to process.

I've made udev packages a special case so that they are always created with a
status of FAILED, thus preventing the script from attempting a diff.