Beware, “Beasts of the Southern Wild” has the power to burst in your mind and bury itself in your heart for weeks to come. A well-deserving winner at both the Cannes (it won the Camera D’Or, a prize exclusively attributed to first-time efforts) and Sundance Film festivals, this triumph of a movie from debuting director Benh Zeitlin is as fierce and moving a film as I can remember seeing in years. And at its center is a performance of sheer deter-