Reverend Billy climbed to the roof of the Pavilion building in Union Square last night around 6:30 p.m. to hang a banner reading: Not For Sale. While he was up there, he gave the passersby a lesson on why the historic free speech structure cannot be turned into a private, upscale restaurant; reminding people that the first Labor Day in 1882 took place there, and that one "shouldn’t have to buy a $15 appetizer to......