An air of poetry hangs over Ain’t Them Bodies Saints, a film that echoes both Days of Heavens and Bonnie and Clyde in its elegiac visual beauty and its mythological feel for rural America. Although set in the early 1970s — in Texas, like the other two pictures (though all three were shot predominantly in other locations) — the film has the same Depression-era look and atmosphere as its predecessors — and the same eye for plain-spoken, inchoate characters whose restless spirits push them to…