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   If the programmer did not provide a name [_i] is used (where [i] is
   the producer's position in the right hand side).

   This syntax modification actually simplifies the code:
   - There is no more on-the-fly naming of unnamed arguments.
   - Inlining is no more restricted to semantic actions that do not use $i.

   The patch is large because:
   - This change has an impact on many modules.
   - The expected results of the bench had to be updated.

Updated the lexer accordingly.
This has the benefit that a type error in a trailer will be correctly located
in the .mly file. Until now, it wasn't.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svnroot/menhir@320 0f8b5475-4b4e-0410-85a8-ee3154a6bfe7