[Oneiric-Topic] Packaging branches

[Robert Ancell]

We currently maintain most Ubuntu Desktop packages in bzr branches and
use bzr-builddeb in merge mode [1] with packaging stored in
lp:~ubuntu-desktop/package_name/ubuntu.  The other option was to use
normal mode [2], but this was not chosen at the time due to the size of
checkouts.

My experience since moving to bzr branches:
- Much, much faster updating of packages
- Branching packages is possible (e.g. working in a PPA)
- Patches are a little bit harder to do, as the branch doesn't contain
the files from the source tarball
- People are often ignoring the branches and uploading directly (or
forgetting do a bzr push) which means changes are sometimes dropped by
accident
- People often do merge requests to lp:ubuntu/package_name, even when
there is a packaging branch

So, I propose that we move all the current packaging branches to using
lp:ubuntu/package_name branches.  We have a few branches using this mode
and have had good success with them.

Some issues that will remain:
- It is possible to screw up the branches so that bzr merge-package
throws a confusing error (I keep doing it).  Perhaps we need some hooks
in bzr to stop this from occurring.  If it can be broken, it will be
broken (repeatedly).
- Branches with a lot of history take a lot of time/bandwidth to check
out.  This adds a barrier to contributors, but is something that bzr
hopefully will solve in the future [3]

--Robert

[1] http://jameswestby.net/bzr/builddeb/user_manual/merge.html
[2] http://jameswestby.net/bzr/builddeb/user_manual/normal.html
[3] https://bugs.launchpad.net/bzr/+bug/46561