INT 2F - Kingswood TSR INTERFACE - COMPATIBILITY MODE

	AX = 3900h
Return: AL = status
	    00h not installed
	    FFh one or more TSRs using this interface is installed
		DX may be destroyed
Note:	this function is provided to that the multiplex number will appear used
	  to other programs
SeeAlso: AH=39h/BL=00h