vlist_realloc (vlist, n)
     VARLIST *vlist;
     int n;
{
  if (vlist == 0)
    return (vlist = vlist_alloc (n));
  if (n > vlist->list_size)
    {
      vlist->list_size = n;
      vlist->list = (SHELL_VAR **)xrealloc (vlist->list, (vlist->list_size + 1) * sizeof (SHELL_VAR *));
    }
  return vlist;
}