NOUAKCHOTT (Reuters) - Mauritanian police detained several suspects and scoured the south of the Saharan country on Tuesday in a hunt for three gunmen who killed four picnicking French tourists in a Christmas Eve attack, officials said. Authorities initially said robbery appeared to be the motive behind Monday's shooting at Aleg, 250 km (160 miles) southeast of the capital Nouakchott, in which turbanned gunmen armed with automatic rifles killed three members of a family and a friend. A fifth member of the French group was injured and survived, Police had not ruled out the possibility the attack was the work...