NAIROBI (Reuters) - Kenyan police fired teargas at more than 1,000 opposition supporters marching through the capital Nairobi on Wednesday to demand election reforms, a Reuters witness said.  Police also used teargas to disperse protesters in the western city of Kisumu, a stronghold of opposition leader Raila Odinga, who on Tuesday announced his withdrawal from a repeat presidential vote scheduled for Oct. 26, citing concerns over fairness. A Reuters witness in Kisumu said the crowd had refused to disperse after being addressed by the county governor.  