INT 21 - Phar Lap 386/DOS-Extender - SET REAL-MODE INTERRUPT VECTOR

	AX = 2505h
	CL = interrupt number
	EBX = CS:IP of real-mode interrupt handler
Return: CF clear
Note:	this function is also supported by FlashTek X-32VM
SeeAlso: AX=2503h,AX=2504h,INT 31/AX=0201h