help: provide a more helpful message when no keyword are matched Before this changeset, when no topic were matching the provided keyword ( in command such as `hg help --keyword babar`) the output was empty. This is confusing and unhelpful for new users seeking assistance in the help. We now display: $ hg help --keyword babar abort: no matches (try "hg help" for a list of topics) This send users in a new direction where they may find what they are looking for.