docs: def open_url(url, headers=None):
      """
      Opens a URL. If headers are passed as argument, no check is performed and
      the URL will be opened.
  
      @param url: the URL to open
      @type url: string
  
      @param headers: the headers to use
      @type headers: dictionary
  
      @return: a file-like object as returned by urllib2.urlopen.
      """
      request = urllib2.Request(url)
      if headers:
          for key, value in headers.items():
              request.add_header(key, value)
      return URL_OPENER.open(request)