An American entry at last year’s “Un Certain Regard” section, Annie Silverstein’s “Bull” wants to be an authentic portrayal of teen angst in a rural and impoverished Texan town. The film is driven by an impressively concise and unemotional performance from Amber Havard, playing the fatherless 14-year-old protagonist, Kris, whose mother (Sara Albright) is behind bars. Grandma (Keeli Wheeler) takes over legal guardian duties, but she can only do so much as Kris has a knack of hanging with the wrong crowd in her south Texan neighborhood.