instance method copy_to

# File actionmailer/lib/action_mailer/vendor/tmail-1.2.3/tmail/port.rb, line 117
    def copy_to( port )
      if FilePort === port
        copy_file @filename, port.filename
      else
        File.open(@filename) {|r|
        port.wopen {|w|
            while s = r.sysread(4096)
              w.write << s
            end
        } }
      end
    end