By David Rooney Chief Film Critic There may be no more fertile ground for screen horror than the enchanted woodlands of the Emerald Isle, which makes it disconcerting when Hokum — a title not entirely inaccurate — opens with a desert scene that’s like an outtake from Sirat. At least until Austin Amelio staggers into the shot in 16th-century conquistador armor, holding an ancient parchment with what appears to be a treasure map. That cumbersome framing device would be superfluous if not for some minor rewards at the end, marking the redemption of a troubled man and his hard-won self-forgiveness. But it’s also symptomatic of the frustrations of writer-director Damian McCarthy’s diffuse script, which piles on story points and portentous symbols but fails to elucidate the underlying mystery.…