“Law Abiding Citizen” is the sort of movie Mel Gibson or Clint Eastwood might have made back in the day — a man survives the slaughter of his family by thugs and sets out to get even, and then some. Gerard Butler is Clyde, a “tinkerer” stabbed during a home invasion. Jamie Foxx is the ambitious prosecutor who lets one of the killers get off easy. Ten years later, Clyde starts killing crooks and the legal eagles who kept them from justice. His battle-of-brains-and-wills scenes with Foxx don’t have a lot of snap, and since those confrontations are the heart here, that drains some energy off the film. But we know exactly what we’re getting — a “who dies next?” slasher film masquerading as a revenge thriller.