Sharon Behn KABUL — Millions of Afghans are being asked to defy Taliban threats and cast their votes Saturday for a new president. But Afghans and analysts say that their biggest fear is that the elections will be marred by fraud, and losing candidates will not accept the results. That, in turn, could lead to greater unrest, instability and violence. So far, there are three front runners: Ashraf Ghani, a former World Bank official, Abdullah Abdullah, a former foreign minister, and Zalmai Rasoul, also a former foreign minister. Apart from differences in personal style – Ghani is seen as a rigid stickler for form, Abdullah as a well-dressed aristocrat, and Rasoul as a reserved…