Verification chaining should call the error init code

[ddeclerck]

Generated verification code should be embedded in error initialization/management code (or a variation of it), as follows:

#ifdef FLG_MULTITHREAD
  init_erreur(irdata);
  if (setjmp(irdata->jmp_bloq) != 0) {
    return irdata->discords;
  }
  /* verification code */
  return irdata->discords;
#else
  init_erreur();
  if (setjmp(jmp_bloq) != 0) {
    return discords;
  }
  /* verification code */
  return discords;
#endif /* FLG_MULTITHREAD */
}

For now, this is done using wrappers in static C files.

Alternatively (preferably), we should just use a better error handling mechanism.