INT 2F U - DOS 3.3+ internal - INSTALLABLE COMMAND - EXECUTE
        AX = AE01h
        DX = FFFFh
        CH = 00h
        CL = length of command name (4DOS v4.0)
        DS:SI -> command name buffer (see AX=AE00h)
        DS:BX -> command line buffer (see AX=AE00h)
Return: DS:SI buffer updated
          if length byte is nonzero, the following bytes contain the uppercase
          internal command to execute and the command line buffer contains the
          command's parameters (the first DS:[SI] bytes are ignored)
Notes:  this call requests execution of the command which a previous call to
          AX=AE00h indicated was resident
        APPEND hooks this call