so, you think you know your history. i bet you can't tell me why a former mayor of atlanta, the current mayor of st. augustine, florida, and a veteran of the civil rights movement went for a swim today with sharks at the georgia aquarium. okay, i'll tell you. back in 1964, st. augustine, florida, america's oldest city, was one of its most racially divided. cruelly so. for some reason, it never gets mentioned in the same breath as selma or birmingham, but it should. blacks were barred from so-called white beaches, and once when a young black man named j.t. johnson dared to jump into a motel swimming pool, the owner poured acid into the water. 46 years later, a new documentary reminds the nation of that event, as well as the bloody night when civil rights marchers were attacked by a segregationist mob, the film is called "crossing in st. augustine" and it premieres tonight at the atlanta film