Joe Leydon Film CriticNo one is more devoted to Australian author Henry Lawson’s “The Drover’s Wife” than Leah Purcell. First, she adapted Lawson’s classic 1892 short story as an award-winning play at Sydney’s Belvoir St Theatre, in which she starred; then she turned it into an acclaimed novel; and now, she has written and directed a gripping film in which she stirringly portrays Molly Johnson, as Purcell colorfully christened the tale’s nameless title character.