def putFatEntry(clus, value)
      raise "DONT TOUCH THIS CLUSTER: #{clus}" if clus < 3
      @stream.seek(@fatBase + FAT_ENTRY_SIZE * clus)
      @stream.write([value].pack('L'), FAT_ENTRY_SIZE)
    end
def putFatEntry(clus, value)
      raise "DONT TOUCH THIS CLUSTER: #{clus}" if clus < 3
      @stream.seek(@fatBase + FAT_ENTRY_SIZE * clus)
      @stream.write([value].pack('L'), FAT_ENTRY_SIZE)
    end
Write a FAT entry for a cluster.