BOSTON — Andrew Bynum showed in the first half tonight exactly why the Lakers should not trade him for Carmelo Anthony. He and Pau Gasol each scored 12 points to keep the Lakers from getting blown out by the Boston Celtics. Bynum made 4 of 6 shots and 4 of 5 free throws and also grabbed three rebounds. The Lakers outscored the Celtics, 28-16, in the paint. They also had 10 second-chance points to only two for Boston. So why were they trailing? They weren’t as good as the Celtics on the perimeter. Ray Allen scored 12 of his 14 points in the first quarter, including a 3-pointer that gave him an NBA-record 2,561. Reggie Miller, who held the previous mark,was courtside as a TNT commentator. Allen and Miller embraced during the break after the first quarter.