Catch invalid argument for usage error

src/libexec/dottum-install

         -n) Action=explore;     shift ;;
         -B) ClobberBroken=false; shift ;;
         -f) ClobberLinks=true;  shift ;;
+        -*) usage -w "unknown argument: $1" ;;
         *)                      break ;;
     esac done
     dottum__route "$@"