Due to an incoming and highly anticipated art exhibit, Alcatraz prison may be harder to get into than out of this fall. Sure, seats are always hard to get on the Alcatraz Cruises ferry, despite the 17 departures a day from Pier 33 in San Francisco. But empty seats may become an even scarcer commodity come Sept. 27, when an installation by art superstar Ai Weiwei opens on the island.Al