By JIMMY GOLEN After decades with the marathon world to itself, the Boston Athletic Association watched races in other cities begin offering prize money and appearance fees and flatter, easier courses that attracted the top talent.The choice was clear for the world's oldest and most prestigious marathon: Accept the changing times, or become an also-ran in the running world.Twenty-five years ago, the organizers of the Boston Marathon signed a sponsorship deal with John Hancock that for the first time provided prize money for the winners - and portable toilets for the masses - and acknowledged what runners had been saying for years: You can't eat prestige."It wasn't just the prize money," said Greg Meyer, whose victory in 1983 remains the last for an American man in Boston.