-- Command: monitor ON/S, OFF/S, ERROR/S, OUTPUT/F
     This command is used to open or close a monitor console window. 
     The monitor, depending on the options given, will display received
     command lines and errors.

        * ON - if given then the console window (or file) will be
          opened.  Both received command lines and error messages will
          be displayed (or saved).  If no options are given then the
          console open state will be toggled.

        * OFF - if given then the console window (or file) will be
          closed.

        * ERROR - if given then the console window (or file) will be
          opened. Only error messages and the associated command line
          will be displayed (or saved).

        * OUTPUT - this argument is used to specify the console output
          device or file.

     Example use of this command:

          monitor on 'cnc:0/660/840/240//auto'
          monitor error 'ram:error.out'
          monitor off