“Tears of the Sun,” set in the midst of a Nigerian revolution, is a rough slog through the jungle, but it builds in intensity and takes on a certain grandeur as it goes along. It’s a military action movie with scenes of blood, slaughter and combat that look authentic. At its best, it’s a little hard to sit through. At its worst, it’s like every other picture about soldiers on a tough mission. What pushes it above mediocrity is that it ends better than it begins. — Mick LaSalle