(Adds details, quotes) By Martyn Herman RIO DE JANEIRO, Aug 19 - Few athletes, not even Usain Bolt, have filled out Olympic stadiums over the past fortnight but pocket-rocket Mariana Pajon did just that on Friday as hordes of Colombians roared her to a second successive BMX gold. On a humpy ribbon of green and red cement at Rio's X Park and with a sea of yellow-shirted compatriots providing a backdrop, she delivered a masterclass to match her London feat. Alise Post of the United States and Venezuela's Stefany Hernandez followed her home but Pajon was in a league of her own. More...