LUCIEN LIBERT RAYMOND Hekking spent decades trying to convince the world that the Mona Lisa painting he bought from a French antique shop in 1953 was the real thing and the one in the Louvre Museum was a fake. Now Christie's auction house has put the 'Hekking Mona Lisa' up for sale, hoping the story of his campaign to realise his dream will help compensate for the fact it is a copy. "It looks like the Mona Lisa but the quality of the execution is not Leonardo da Vinci," Christie's International Director of Old Master Painting Pierre Etienne said. "Unfortunately…