Alice Munro has long been heralded for her penetrating, lyrical prose, and in “The Bear Came Over the Mountain”—the basis for Sarah Polley’s film Away from Her —her prodigious talents are once again on display. As she follows Grant, a retired professor whose wife Fiona begins gradually to lose her memory and drift away from him, we slowly see how a lifetime of intimate details can create a marriage, and how mysterious the bonds of love really are