DOCUMENTARY PREMIERE: Frederick Wiseman is 90 years old now, and still making documentary films. His latest, premiering tonight on PBS, is City Hall, which spends more than four hours of screen time, culled from much more raw footage than that, showing how the city of Boston does the business of running its municipality. Wiseman’s unusual filmmaking approach has been the same since his famous first work, 1967’s Titicut Follies, which looked in depth at another Mas