By Tarek Amara and Angus McDowall TUNIS (Reuters) -Tunisians voted on Monday on a new constitution which critics of President Kais Saied fear will dismantle the democratic gains of the 2011 revolution by handing him nearly total power. The divided opposition urged a boycott, calling Saied’s moves a coup that risks flinging Tunisia back into the autocratic era from before the revolution and putting the final nail into the coffin of the 2011 Arab Spring uprisings. The electoral commission said 13.6% of voters had taken part by 1430 GMT, nine and a half hours into the 16-hour voting period. Howev…