For me, reuinion gigs often fail to satisfy, not because the band can't play anymore but because they're too excited that they can. There's a low, giddy buzz onstage as the band realizes, "We can still do this!" that takes the edge off. Rock 'n' roll's not about smiles. That wasn't a problem for The Afghan Whigs at Tipitina's. Friday night, they went to work with characteristic intensity as if they hadn't stopped.