def update_output_dir(op_dir, time)
      File.open(output_flag_file(op_dir), "w") {|f| f.puts time.rfc2822 }
    end
def update_output_dir(op_dir, time)
      File.open(output_flag_file(op_dir), "w") {|f| f.puts time.rfc2822 }
    end
Update the flag file in an output directory.