Last night, the Foo Fighters headlined Madison Square Garden, and they trotted out a couple of serious rock O.G.s during the encore. First off, Hüsker Dü frontman Bob Mould joined them to help out on "Dear Rosemary," his recent collaboration with the band, and they followed that by covering Tom Petty's "Breakdown." (No Hüsker song, though, sadly.) And when that ...