INT 20 - Minix - SEND/RECEIVE MESSAGE

	AX = process ID of other process
	BX -> message
	CX = operation (1 send, 2 receive, 3 send&receive)
Program: Minix is a Version 7 Unix-compatible operating system by Andrew
	  Tanenbaum
Note:	the message contains the system call number (numbered as in V7
	  Unix(tm)) and the call parameters