Error messages given when working on an unborn branch that is
checked out in another worktree have been improved.
* rj/branch-unborn-in-other-worktrees:
branch: avoid unnecessary worktrees traversals
branch: rename orphan branches in any worktree
branch: description for orphan branch errors
branch: use get_worktrees() in copy_or_rename_branch()
branch: test for failures while renaming branches