PackageDiff.title is bogus for inter-PPA copies

From lib/lp/soyuz/model/packagediff.py:

    @property
    def title(self):
        """See `IPackageDiff`."""
        ancestry_archive = self.from_source.upload_archive
        if ancestry_archive == self.to_source.upload_archive:
            ancestry_identifier = self.from_source.version
        else:
            ancestry_identifier = "%s (in %s)" % (
                self.from_source.version,
                ancestry_archive.distribution.name.capitalize())
        return '%s to %s' % (ancestry_identifier, self.to_source.version)

Saying "(in Ubuntu)" just because it's from another (non-primary) archive is wrong.