Merge branch 'rj/advice-delete-branch-not-fully-merged'

The error message given when "git branch -d branch" fails due to
commits unique to the branch has been split into an error and a new
conditional advice message.

* rj/advice-delete-branch-not-fully-merged:
  branch: make the advice to force-deleting a conditional one
  advice: fix an unexpected leading space
  advice: sort the advice related lists