“When Caitlin Corbett’s new duet ‘Yield’ was subject to a last-minute costume overhaul at the Boston University dance theatre last month so that dancer Nicole Pierce wouldn’t dance topless, the heavy-handed puritanism of the regulation exactly proved the choreographer’s point: our culture is so hypersexualized that we never get a chance to consider female anatomy in a neutral way.” So what are Boston’s regulations about nudity onstage? Turns out it’s complicated…