NAIROBI (Reuters) - Kenya opposition leader Raila Odinga urged supporters to boycott Thursday s repeat presidential election and persuade their friends to do the same, saying his opposition movement would be transformed into a resistance movement against the government.   From today we are transforming the NASA coalition into a resistance movement,  he told a cheering crowd of thousands of people in Uhuru Park in the capital of Nairobi. He wants new elections held within 90 days, he said.  