def nlst(dir = nil)
      cmd = "NLST"
      if dir
        cmd = cmd + " " + dir
      end
      files = []
      retrlines(cmd) do |line|
        files.push(line)
      end
      return files
    end
def nlst(dir = nil)
      cmd = "NLST"
      if dir
        cmd = cmd + " " + dir
      end
      files = []
      retrlines(cmd) do |line|
        files.push(line)
      end
      return files
    end
Returns an array of filenames in the remote directory.