‘Mamma’ gets a box office tune-up

Weekend B.O.: Sing-along screenings bump up musical — “Mamma Mia!” — here you go again. Special Labor Day sing-alongs for Universal’s bigscreen musical adaptation “Mamma Mia!” scored bigtime, with the film actually enjoying a 2% bump in ticket sales over the holiday weekend. That’s impressive, considering the pic was in its seventh sesh.