INT 15 - MultiDOS Plus - SEND MESSAGE TO ANOTHER TASK                           
	AH = 04h
	AL = mailbox number (00h-3Fh)
	CX = message length in bytes
	DS:SI -> message
Return: AH = status
	    00h successful
	    01h out of message memory
	    02h invalid mailbox number
Note:	the message is copied into a system buffer; the caller may immediately
	  reuse its buffer
SeeAlso: AH=05h"MultiDOS"