Cher warbles, Xtina ululates, and Fosse jazz hands are heavily implied. The soundtrack for the pair’s upcoming movie musical Burlesque offers a shamelessly diva-fied mix of balladry, Broadway cabaret, and backroom boogie-woogie with Aguilera especially sounding far more comfortable in the retro-dolly mode of 2006’s Back to Basics than she did on her recent ''futuristic'' misfire Bionic. B