NAIROBI, Oct 13 (Reuters) - The following company announcements, scheduled economic indicators, debt and currency market moves and political events may affect African markets on Thursday. - - - - - EVENTS: *KENYA - The central bank auctions 91-day Treasury bills worth 4 billion Kenyan shillings. GLOBAL MARKETS Asian stocks stumbled to three-week lows and U.S. stock futures and Treasury yields fell after China's September trade data showed a sharp decline in exports, raising fresh