Get handle directory

        Entry:
          AH = 54h
          AL = subfunction
                00h get handle directory
                    ES:DI = pointer to buffer for handle directory
                01h search for named handle
                    DS:SI = pointer to 8-byte name
                02h get total number of handles
        Return:
          AL = number of entries in handle directory (subfunction 00h)
          DX = value of named handle (subfunction 01h)
          BX = total number of handles (subfunction 02h)
          AH = status
            00h successful
            80h internal error
            81h hardware malfunction
            84h undefined function requested
            8Fh undefined subfunction
            A0h no such handle name
            A1h a handle found had no name