Everything about “Capharnaum” looked good, for a while. Nadine Labaki, its talented filmmaker, the trailer (“some squirt with killer looks stands in front of a judge in a Beirut court and tells him, “I want to sue my parents for having given birth to me”), the promise of a social drama examining Lebanese society, a film by a woman, going up for the top prize in Cannes. Labaki set out to make a movie about childhood. When young Zain