NAIROBI (Reuters) - Men in plain clothes fired shots in the air as hundreds of opposition supporters marched through the Kenya s capital to its election board headquarters on Monday, a Reuters witness said. The demonstrators were demanding reforms ahead of a presidential election scheduled for Oct. 26.  Senator James Orengo from the opposition alliance said they also wanted to warn ruling party lawmakers not to pass a proposed amendment to the election laws that would limit circumstances in which the Supreme Court could nullify an election.  