INT 67,56 - Alter Page Map and Call (LIM EMS 4.0+)

	AH = 56h
	AL = 00  physical page numbers provided by caller
		 DX = EMM handle
		 DS:SI = pointer to structure with page map and call address
	     01  segment addresses provided by caller
		 DX = EMM handle
		 DS:SI = pointer to structure with page map and call address
	     02  get page map stack space required


	on return:
	BX = stack space required (AL = 02)
	AH = status  (see EMS STATUS)


	- if successful, the target address is called
	- use a RETF to return and restore mapping context