Rat out name of the disobedient caller

include/core.sh

     case $front in
         warn|debug|die|usage_is)    __echo_$src "$@" | $mkpretty >&2 ;;
         think)                      __echo_$src "$@" | $mkpretty     ;;
-        *)                          echo "do not call __echo* directly" >&2; exit 2 ;;
+        *)      echo "do not call __echo* directly: $internal" >&2;
+                exit 2                                               ;;
     esac
 }