As Paul Pierce can tell you, getting to the line is equal parts aggression and art. It’s a mix of drive and body English. Some, after years of watching the Celtics captain lunge and gyrate through the lane, would call it acting. But Rajon Rondo is still attempting to develop his own thespian style. As a testament to the unevenness of the Celtics point guard’s track record at the free throw line, he didn’t attempt his first free throw of the preseason until the second half of the fourth exhibition game last week in New York.