When the Cannes film festival opens, it opens with the traditional trappings: Hordes of photographers, celebrities, curious fans and more photographers; lots of big film deals being pitched over Mediterranean lunches; topless beauties sunning themselves on the beach; and a major new film premiere. Cannes has been suffering lately--last year's attendance was down, with lots of buyers and sellers opting instead for Los Angeles' American film market--but when Cannes kicked off this week it was able to provide three of the four standbys. What the festival lacked was a hot new film to open the proceedings the way Steven Spielberg's "The Extra Terrestrial" will close them. So the organizers decided to go for a bit of history: They presented D.W. Griffiths' 66-year-old, nearly three-hour epic "Intolerance." Francis Coppola showed with "Napoleon" that old silent-film clasics can be potent attractions these days, and if it could work for Coppola--for whom not too much has gone right lately--then it should certainly have worked for Cannes. But it didn't. Griffiths' film--shown to the accompaniment of 82-year-old Stanley Kilburn on piano--immediately sent more people into the lobby and the streets than it kept in the theater. The festival director tried to explain that it was dinnertime and all those people were probably hungry, but director Billy Wilder came up with the best explanation. "They didn't want to see 'Intolerance,' " he quipped. "They wanted to see Pia Zadora."