"bzr upgrade" should do conversion outside of .bzr

[Jelmer Vernooij]

It would be useful if "bzr upgrade" could do a conversion in a different directory than .bzr and only as the last part of the process replace .bzr/ with that directory.

This would mean that it is no longer possible to end up with a only partially converted .bzr directory if something fails halfway through.

Users would still be able to access the repository while the upgrade was happening. Perhaps the permissions should be changed to disallow new revisions from being added though, since new revisions would not end up in the newly created repository.

You would also always know that you can remove a backup.bzr directory, since you can be sure that the .bzr directory has all revisions. Barring bugs in the upgrade process you wouldn't have to be renaming directories to .bzr if a backup fails halfways through - you only would have to remove the upgrade.bzr (or whatever we would end up calling it) directory.