Writer-director Brian Helgeland delivers his best movie with “42,” a sharp, earnest tale about Jackie Robinson’s contributions to Major League Baseball. Although Robinson was an outstanding player who appeared in six consecutive All-Star Games, he is best remembered as the man who broke the color barrier. In “42,” Helgeland deftly tells the story of Robinson’s signing, as well as the pressure both he and Rickey faced once the color barrier was broken.