INT 2D - DTown Utilities v1.40+ - MEMORY VIEW SET REFERENCE

	AL = 51h
	BL = reference ("bookmark") number
	CX:DX = new address for reference
Return: AL = status
	    00h invalid index
	    FFh reference set
Note:	this function is only available if the extended API has been installed
	  in the resident portion
Program: DTown Utilities is a shareware programmer's utility TSR by Jeroen van
	  Disseldorp
SeeAlso: INT 2D/AL=10h"DTown",INT 2D/AL=20h,INT 2D/AL=50h