[rfc] upgrade pqm chroot to lucid

[Martin Pool]

I'm going to ask our sysadmins to upgrade bzr's pqm chroot to run
Ubuntu Lucid (from Hardy).  Lucid 10.04 is the most recent
long-term-support release.

The immediate motivation for this is so that we can get python-sphinx
running there and checking that the documentation builds.

More generally, if we add new optional dependencies, we may want tests
to run against them in pqm and this will be more easily done on more
recent releases.

The main drawback of this is that pqm will no longer run python2.4.

There's no single platform where we can test every single python
interpreter and combination of libraries we want to support.  I think
we should run pqm on the platform that's easiest to maintain, and
that's closest to our typical/normal case, and Lucid is ahead on both
counts.  Then we can use Babune to guard against regressions on less
central platforms.

If anyone thinks this is unbearably bad, say so.

-- 
Martin