I’ve long thought that Hanover police arrest Dartmouth students for underage drinking to make money for the town. Maybe pumping up the town coffers isn’t the cops’ only motivation, though. Arresting underage drinkers can be quite the power trip, too, or so it seems from a recent case. In underage drinking cases involving 18- to 20-year-olds, Hanover cops decide who goes to court and who doesn’t. Students who don’t play …