convert/bzr: convert all branches (issue3229) (BC) Instead of opening the target bzr checkout as a single branch, we try to open it as a repository. This has the following effects: - All branches are now converted - bzr branch names are preserved. Previously, the selected branch was always converted as 'default'. Branches without a name or 'trunk' are mapped to 'default branch. - Lightweight checkouts are no longer supported. Maybe they can be, I did not try to fix that at all. Implementation notes: - This was a quick fix, I have no knowledge of bzr API besides browsing 2.0.3 sources. - The fix was only tested on OSX against bzr 2.4.2. - Tags discovery does not handle collisions. I have no idea how tags work in bzr so maybe such collisions are not possible.