“The Godfather’s Revenge” cruises through a few scenes of double-dealing and then invariably drops some thundering reference to scenes mostly remembered from the Francis Ford Coppola movies. When Johnny Fontane and Francesca Corleone stroll in the moonlight, for instance, they end up flirting on top of the grave of Khartoum, the racehorse whose head showed up in “The Godfather.” This made me want to put down the book and go watch the original scene on YouTube.