INT 2F U - DOS 4+ XMA2EMS.SYS extension internal - GET HIDDEN FRAME INFORMATION
        AH = 1Bh
        AL <> 00h
        DI = hidden physical page number
Return: AX = FFFFh if failed (no such hidden page)
        AX = 0000h if OK, then
             ES = segment of page frame
             DI = physical page number
Notes:  this corresponds to the data edited out of the INT 67/AH=58h call
        FASTOPEN makes this call with AL = FFh