FACTBOX - Main candidates in Afghanistan's presidential election --- (Reuters) - Afghanistan holds a presidential election on April 7 to elect a successor to Hamid Karzai. --- Here are brief descriptions of the three leading contenders. --- ASHRAF GHANI AHMADZAI, ZALMAY RASSOUL, ABDULLAH ABDULLAH - More, at: http://in.reuters.com/article/2014/04/02/afghanistan-candidates-election-idINDEEA3104Q20140402