NOW THAT SO MANY MEN ARE BEING brought to account for past misbehavior, we’re all asking questions we never thought to ask before. One that comes up a lot is: What was he thinking? It’s early yet, but Chappaquiddick, director John Curran’s suspenseful, disturbing account of Senator Ted Kennedy’s involvement in the 1969 drowning death of 28-year-old campaign worker Mary Jo Kopechne, may be the most What was he