rxtx import is interestingly broken - UDD importer can pull from the past

spiv and I have, in the course of trying to unbreak the rxtx import, discovered another bug which has resulted in the import being left in a rather odd state - hence this bug to track it.

The problem is that bzr-builddeb's divergedness checking code has a bug where it checks for *divergence* but does not check whether the non-diverged pull candidate is ahead or behind of the current branch last revision. As a result, it is possible for it to pull in a direct Debian import branch into an Ubuntu branch, eliding Ubuntu history in the case where a package formerly had an Ubuntu delta, but is now a direct sync from Debian again.

In rxtx's case, this manifests as the oneiric branch not being a subset of the natty branch.

How we need to fix this:

1) Fix bzr-builddeb's code
2) Get bzr-builddeb updated on jubany
3) pull --overwrite the oneiric branch with the hardy branch
4) Cleanup all tags in branches which are not in the ancestry of the branch last revision
5) requeue_package.py --full --force rxtx