Overture Center is facing a $3 million deficit; if you want to spend some money and help the downtown arts district get off its financial knees, why not go see Avenue Q (now through October 26?) It is that rare thing — a big musical which is not either a retread of songs everybody knows (Movin’ Out, Mamma Mia) or a thin coat of “edgy” on a boring Broadway chassis (yes, you, Urinetown.) Avenue Q has jokes. Funny jokes! Also puppets that have sex.