Instantiate the editor CMDL with a dummy I/O port that signals an

Instantiate the editor CMDL with a dummy I/O port that signals an
error if it is read from or written to.  Define the CHILD-PORT
operation on that CMDL so that spawning a another CMDL under the
editor CMDL (e.g. by DEBUG-INTERNAL-ERRORS? being true) will cause the
child to use the port that was in effect when the editor was started.