MANAMA/GENEVA, Dec 30 (Reuters) - The head of Bahrain's main Shi'ite Muslim opposition group, detained on Sunday after leading a protest rally over last month's elections, has been remanded in custody for a further week, a group official said on Tuesday. In Geneva, the United Nations human right ****** said it was concerned at the detention and potentially lengthy prison sentence that could be handed to Sheikh Ali Salman, secretary general of al-Wefaq Islamic Society. ...