Guatemalans head to the polls Sunday in a presidential runoff marked by the harassment of a surprise frontrunner, who has fired up voters with his promises to end the rot of corruption.The corrupt "have progressively taken control of all state institutions," former attorney general Claudia Paz y Paz -- who is now in Costa Rica -- told AFP. The first round in June saw low voter turnout and more than 17 percent of ballots cast invalid, with little hope among Guatemalans that their fortunes would c