Bison exp is broken

[Akim Demaille]

but it is on purpose.  I have deeply changed the handling of EOF: now
the initial rule ($axiom : START-SYMBOL EOF) is explicit, and no
longer preformed by hand in different places.

But as a result, the final state is no longer the last state (in the
sense that it's number is no longer the highest number).  Many things
change, and I would not be surprised some things are broken.

But this is the right track.  Please, be patient, I am going to fix
the test suite, as I make sure the behavior is really correct.

In other words, if something no longer works, it is not OK, please
warn me: AFAIK, only the test suite should be broken.