INT 21 P - Phar Lap 386/DOS-Extender - GET SEGMENT LINEAR BASE ADDRESS          
	AX = 2508h
	BX = segment selector
Return: CF clear if successful
	    ECX = linear base address of segment
	CF set if invalid segment selector
Note:	this function is also supported by FlashTek X-32VM
SeeAlso: AX=2509h