KABUL (Reuters) - Forces of a renegade adviser to President Hamid Karzai overran the capital of a northern province of Afghanistan on Thursday, creating a fresh security headache for the government and its U.S.-led foreign backers. General Abdul Rashid Dostum's largely ethnic Uzbek militia invaded Faryab from neighboring provinces on Wednesday, prompting the central government to send national troops there on Thursday in an attempt to maintain control. The fighting in the north and another outbreak in the western province of Herat last month have been an unwanted diversion for Karzai and U.S.-led forces in Afghanistan even as they battle...