Reallocate Extended Memory Block (Function 0Fh)

        ARGS:   AH = 0Fh
                BX = New size for the extended memory block in K-bytes
                DX = Unlocked extended memory block handle to reallocate

        RETS:   AX = 0001h if the block is reallocated, 0000h otherwise

        ERRS:   BL = 80h if the function is not implemented
                BL = 81h if a VDISK device is detected
                BL = A0h if all available extended memory is allocated
                BL = A1h if all available extended memory handles are in use
                BL = A2h if the handle is invalid
                BL = ABh if the block is locked

This function attempts to reallocate an unlocked extended memory block
so that it becomes the newly specified size.  If the new size is smaller
than the old block's size, all data at the upper end of the old block is
lost.