Fortify against some bad scenarios

src/include/pretty.sh

         _pretty__is_internal && continue
         _pretty__is_frontend && echos "$fname" && return 0
         echo "do not call _pretty_* directly: $fname" >&2
-        return $FFOO_EXIT_USAGE
+        return "$FFOO_EXIT_USAGE"
     done
 }
 
     # Print command line, launch it and report exit status
     #
     local c=\$
-    test $(id -u) -eq 0 && c=\#
+    test "$(id -u)" -eq 0 && c="#"
     echo "$c $*"
     "$@"
     echo "^ exit status: $?"