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

	AX = 2511h
	DS:EDX -> parameter block (see #01361)
Return: all segment registers unchanged
	EDX unchanged
	all other registers contain values set by the real-mode int handler
	the flags are set as they were left by the real-mode interrupt handler
	real-mode register values are returned in the parameter block
Note:	this function is also supported by FlashTek X-32VM
SeeAlso: AX=2503h,AX=2505h,AX=250Eh,AH=E3h"OS/286",INT 31/AX=0300h