KANDAHAR, Afghanistan (Reuters) - Afghan security forces have captured Taliban leader Mullah Mohammad Omar's personal security chief as he travelled in a van to the southern city of Kandahar, provincial officials have told Reuters. The capture of Toor Mullah Naqibullah Khan, who headed Mullah Omar's household security, could help U.S. and Afghan forces track down his boss, one of the most wanted fugitives in the U.S.-led war on terror. Osama bin Laden, who ran his al Qaeda network in Afghanistan under the protection of the Taliban, is also believed to be at large in the region. "We have arrested top...