OSSINING, N.Y. (AP)--Pete Seeger was in New York City's Union Square in 1953 along with 5,000 other supporters of Julius and Ethel Rosenberg as the hour of the couple's execution drew near. ``We were waiting and hoping Eisenhower would give a last-minute reprieve,'' says Seeger, now 84. ``We learned that wouldn't happen, and then a great sigh, a great wail went up from the crowd when the time came and we knew they'd been executed.'' On the 50th anniversary of the execution Thursday, Seeger, Susan Sarandon, Harry Belafonte and other show business activists will appear at a benefit for the...