def mtime(filename, local = false)
      str = mdtm(filename)
      ary = str.scan(MDTM_REGEXP)[0].collect {|i| i.to_i}
      return local ? Time.local(*ary) : Time.gm(*ary)
    end
Returns the last modification time of the (remote) file.  If +local+ is
+true+, it is returned as a local time, otherwise it's a UTC time.