code: def already_downloaded(filename):
      
      cur_file = os.path.join(c.bview_dir, filename)
      old_file = os.path.join(c.bview_dir, 'old', filename)
      if not os.path.exists(cur_file) and not os.path.exists(old_file):
          return False
      return True
docs: Verify that the file has not already been downloaded.