INT 13 - IBM/MS INT 13 Extensions - INSTALLATION CHECK

	AH = 41h
	BX = 55AAh
	DL = drive (80h-FFh)
Return: CF set on error (extensions not supported)
	    AH = 01h (invalid function)
	CF clear if successful
	    BX = AA55h if installed
	    AH = major version of extensions
		01h = 1.x
		20h = 2.0 / EDD-1.0
		21h = 2.1 / EDD-1.1
		30h = EDD-3.0
	    AL = internal use
	    CX = API subset support bitmap (see #00271)
	    DH = extension version (v2.0+ ??? -- not present in 1.x)
Note:	the Phoenix Enhanced Disk Drive Specification v1.0 uses version 2.0 of
	  the INT 13 Extensions API
SeeAlso: AH=42h"INT 13 Ext",AH=48h"INT 13 Ext"