INT 2F - DOS EXTENDER INSTALLATION CHECK                                        
	AX = F100h
Return: AL = FFh if DOS extender present
	    SI = 444Fh ("DO")
	    DI = 5358h ("SX")
Note:	supported or soon to be supported by Phar Lap, Rational, Ergo, and IGC
SeeAlso: AH=A1h,AX=ED00h,AX=FBA1h/BX=0081h,INT 15/AX=BF02h