One of the most fertile subjects of contemporary European cinema is the desolation of contemporary European life. The extravagance and high spirits outside the Cannes screening rooms thus frequently stand in jarring contrast to the misery displayed within them, where stories of privation, disconnection and violence hold up a corrective mirror to a continent that likes to present itself to the rest of the world as prosperous, unified and at peace. A.O. Scott and Manohla Dargis reports.