Merge branch 'jc/branch-in-use-error-message'

"git branch -f X" to repoint the branch X said that X was "checked
out" in another worktree, even when branch X was not and instead
being bisected or rebased.  The message was reworded to say the
branch was "in use".

* jc/branch-in-use-error-message:
  branch: update the message to refuse touching a branch in-use