What’s plucked from the dirt can’t come clean no matter how hard it’s washed out. The heart of Alain Guiraudie’s new comedic thriller, “Misericordia,” is rotten, beautiful and certainly pulled from a soil that can never be discarded.  “Misericordia” follows a young man named Jérémie as he returns to his small hometown Saint-Martial after his former boss dies. Jérémie stays with the widow of his boss, which angers her son until the tensions boil over, and the whole town starts falling apart at the seams.  Guiraudie is a mischievous filmmaker. The central tensions at the heart of “Misericordia,” which he wrote and directed, are deeply knotty and often unspoken for long stretches of time. His preoccupations with death and desire are quite apparent as the two often overlap and lead to erotic and disastrous results alike.  Within this very small town of Saint-Martial, Guiraudie builds a whole world. Everybody knows each other, therefore, a glance can be treacherous, and secrets are never...