Code review comment for lp:~nmb/bzr/893470-dedupe-list-branches

Hi Neil,

If you care about duplicates in BzrDir.list_branches(), I think we should just fix that API.

This fix eliminates duplicates - but only for the default branch. We should be consistent and remove dupes for the other branches as well, if we're doing that.

An alternative fix for this (rather than checking afterwards) might be to just have a way to exclude all branch references.