In 1980, Ringo Starr accepted a role in the movie "Caveman" for United Artists.         The cast included old school comics including Avery Schreiber (best known at the time for game shows and a long running series of Doritos commercials), Jack Gilford (a veteran actor of over 40 years at the time), and relative newcomers including Shelley Long, Dennis Quaid and Oakland Raider John Matuszak.      The thin plot, and lack of dialogue (the script consists of roughly two dozen words for concepts such as fire, love, dinosaur and sexual congress).      The film might lay alongside other Ringo projects, were it not for the fact that it introduced Ringo to Barbara, and resulted in their love affair and marriage less than a year later.