Jack Nicholson is the Hollywood celebrity who is most like a character in some ongoing novel of our times. At the age of 37, he learned that the woman he had always believed to be his mother was his grandmother and that his two older sisters were really his mother June and his Aunt Lorraine. The soap opera-like twist was worthy of "Chinatown" (1974) a la Evelyn Mulwray (Faye Dunaway): "She's my sister. . . she's my daughter. . . she's my sister and my daughter." Indeed, the timing of his discovery could have influenced that screenplay written by friend Robert Towne, unless it was just balmy