The world probably would be a better place if we all kept our mouths shut. Or, at least that’s the takeaway from “The Insult,” the Oscar-nominated courtroom drama from former Quentin Tarantino sidekick Ziad Doueiri.In it, the Lebanon native takes a harsh look at his homeland and the uneasy alliance between the ruling Christians and the ever-expanding Muslim population, many of whom are exiled Palestinians.