INT 10,5 - Select Active Display Page

	AH = 05
	AL = new page number, see VIDEO PAGES

	for PCjr only:
	AL = 80h to read CRT/CPU page registers
	     81h to set CPU page register
		 BL = CPU page register
	     82h to set CRT page register
		 BH = CRT page register
	     83h to set CPU and page registers
		 BH = CRT page register
		 BL = CPU page register


	on return: (PCjr only)
	BH = CRT page register
	BL = CPU page register