NAME
        CMD_FLUSH -- abort all I/O requests (immediate)

   FUNCTION
        CMD_FLUSH aborts all stopped I/O at the unit.

   IO REQUEST
        io_Message      mn_ReplyPort set if quick I/O is not possible
        io_Device       preset by the call to opendevice
        io_Command      CMD_FLUSH
        io_Flags        IOB_QUICK set if quick I/O is possible