* spot/parseaut/parseaut.yy, spot/parseaut/parsedecl.hh,
spot/parseaut/public.hh, spot/parseaut/scanaut.ll: Use a reentrant
scanner, so that we can now parse multiple automaton streams at the
same time.  This is needed for the future autcross, which is going to
read several individual automata produced by different tools, while
reading the stream of automata to process.