By Elizabeth Piper KIEV (Reuters) - In late February, just two days after pro-Russian president Viktor Yanukovich fled Kiev, Ukraine's parliament repealed a law enshrining the rights of Russian-speakers to use their first language. Ukraine's Russian speakers, concentrated in the east and the south where the law applied, viewed the action as vengeful. In Moscow, Russia's leaders saw an opportunity. Ukraine's new rulers took just five days to reverse course to once again allow the use of Russian in some schools, courts and other state institutions.