Upgrading via the desktop installer (ubiquity)

[Evan Dandrea]

In 11.04 and later versions, the desktop CD installer (ubiquity)
presents an option to upgrade Ubuntu if it finds a single copy on the
system.  This functionality is not exactly equal in operation to
upgrade-manager, nor does it share much code with that application.

Such an upgrade will first make a backup of apt's state, including
repacked debs (using dpkg-repack) for any packages that it cannot find
a source for.  Following this, it will delete all non-user and
non-local files on the existing partitions.  This is roughly
everything but /usr/local, /var/local, /usr/src, and /home. It will
then install Ubuntu over top of the partially-cleared directory
structure and install the packages referenced in the apt state backup.

When triaging upgrade bugs, please make sure they're targeted to and
have logs for the correct package.  If the user upgrades via the
option in the desktop CD installer, change the package to ubiquity and
have the user run `sudo apport-collect $bug_number`.

Thanks,
Evan