The second part of the Cannes Festival is turning out to be more challenging, quality-wise, than the first where “Ma Loute” and “Mal de Pierres,” an off-kilter comedy and a love drama respectively, were easy to stamp as good cinema. Week two, on the other hand, isn’t all gems. Yesterday, the Dardenne Brothers’s “La fille inconnue” (“The Unknown Girl”) received a lukewarm response. It's a drama about a young woman doctor who, overcome