- one automata example added
 - changed the reset condition in node calls (now a simple bool expr)
 - bug corrected in clock calculus
 - bug corrected in traceability info
 - added field in variables to test whether they are original 
   or created by normalization process: better error message 
   for causality problems

 Warning: this is the first working version of automata, needs further 
 testing (and debugging). AFAIK, the semantics is close to Lustre V6,
 but further changes may be needed to equate them.