The child is very much father to the man in “Staying Vertical,” a serenely nutty cinematic pastoral that unfolds at the crossroads of life and death, freedom and responsibility, this world and the next. The film follows a screenwriter in his 30s named Leo into the open countryside, where he shacks up with a shepherdess, has a baby boy and soon finds himself dealing with much more than just a crippling case of writer’s block.