INT 21 - Phar Lap 386/DOS-Extender - SET INT TO ALWAYS GAIN CNTRL IN PR. MODE

	AX = 2506h
	CL = interrupt number
	DS:EDX = CS:EIP of protected-mode interrupt handler
Return: CF clear
Notes:	this function modifies both the real-mode low-memory interrupt
	  vector table and the protected-mode Interrupt Descriptor Table (IDT)
	interrupts occurring in real mode are resignaled in protected mode
	this function is also supported by FlashTek X-32VM