Ever since his smash in Saturday Night Fever, John Travolta has taken heat for making too many movies that show off his body and little else. None of that here. As a cabdriver named James in this witless farce, written and directed by Amy Heckerling (Fast Times at Ridgemont High), Travolta looks puffy and pooped. But, oh, is he sensitive. James helpfully speeds Mollie (Kirstie Alley of Cheers), an unmarried, pregnant CPA, to the delivery room. Later, he babysits, offers moral support, friendship…