The queasily enjoyable fiction film “The Last King of Scotland,” based on the novel by Giles Foden and directed by Kevin Macdonald, creates a portrait of the famous Ugandan dictator Idi Amin from inside the palace walls. Furiously paced, with excellent performances by Forest Whitaker as Amin and James McAvoy as the foolish Scotsman who becomes the leader’s personal physician, the film has texture, if not depth and enough intelligence to almost persuade you that it actually has something of note to say. The film makes the case that Amin was rational enough to understand his country’s tangled relationship with British imperialism and to inject that sociopolitical understanding into words.