INT 21 - Phar Lap 386/DOS-Extender - SET REAL- & PROTECTED-MODE INT VECTORS

	AX = 2507h
	CL = interrupt number
	DS:EDX = CS:EIP of protected-mode interrupt handler
	EBX = CS:IP of real-mode interrupt handler
Return: CF clear
Notes:	interrupts are disabled until both vectors have been modified
	this function is also supported by FlashTek X-32VM
SeeAlso: AX=2504h,AX=2505h