This past May 14th, the Mississippi-born, Chicago-bred rocker marked his 49th year in the music business: it's been that long since "Bo Diddley" debuted on the R&B charts and sent an electric volt through jukeboxes across, America. And he hasn't quit, either. When we called his Florida residence for this exclusive interview, he was in the studio. ''Man, I don't even know what I'm playing," he laughed "I ...