* Wiggins seals eighth Olympic medal * Britain win thriller against Australia (Adds details) By Martyn Herman RIO DE JANEIRO, Aug 12 (Reuters) - Bradley Wiggins fired Britain to track cycling team pursuit gold in a titanic final battle with Australia at the Rio Games on Friday, etching his name into the record books as the most decorated British Olympian of all time. The icing on the cake for the quartet of Wiggins, Ed Clancy, Steven Burke and Owain Doull was breaking the world record twice in the space of a few pulsating hours at Rio's velodrome. More...