By Tom Perry BEIRUT (Reuters) - With moderate rebels facing defeat by al Qaeda in Syria's **rth, groups holding a corner of the south are seeking a higher profile and more help, as the last Western-backed forces holding out against both President Bashar al-Assad and the jihadists. The southern rebels, described by Western officials as the best organized of the mainstream opposition, say they are the last hope for a revolution hijacked by jihadists. In recent days they have laid out a transition plan for a Syria without Assad, taking on a political role that in the past they left to others. ...