Richard O’Brien’s stage musical, “The Rocky Horror Show,” a sexually-unabashed parody of sci-fi films, was turned into a movie in 1975 – and it bombed. But fans at midnight showings turned it into a cult favorite that is still running 50 years later – with audience participation a major draw. Tracy Smith talks with actors Tim Curry and Barry Bostwick, producer Lou Adler, and film scholar Jeffrey Weinstock about the movie’s very long legs.