INT 2F CU - DOS 5+ - FLOPPY-DISK LOGICAL DRIVE CHANGE NOTIFICATION              
	AX = 4A00h
	CX = 0000h
	DH = new drive number
	DL = current drive number
Return: CX = FFFFh to skip "Insert diskette for drive X:" message
Note:	called by MS-DOS 5.0+ IO.SYS just before displaying the message
	  "Insert diskette for drive X:" on single-floppy systems