BOSTON — The Lakers and the Boston Celtics played another game of trench warfare tonight in Game 4 of the NBA Finals. It’s not pretty basketball. It’s kind of ugly. The Lakers don’t seem to mind, though. Pau Gasol got down and dirty in the first half, scoring a team-leading 13 points. He made 3 of 6 shots and 7 of 8 free throws. Kobe Bryant added 12 points, including eight during an electric stretch in which he scored on three straight possessions and gave the Lakers the lead for good in the half. Andrew Bynum played only 11 minutes in the first half and scored two points and grabbed two rebounds.