INT 2F - PRINDIR v9.0 - SET ECHO STATE                                          
	AX = 7F0Ch
	DX = new state (00h echo off, 01h echo on)
Return: AX = status
	    0000h successful
SeeAlso: AX=7F00h"PRINDIR",AX=7F0Ah,AX=7F0Bh,AX=7F0Dh,AX=7F0Eh