message: elle.print: Don't rely on printf.
diff: @@ -62,7 +62,8 @@ namespace elle
  bool
  branch_test(T const& t, ...)
  {
  - elle::err("type is not a truth value: %s", elle::type_info<T>());
  + elle::err(elle::print("type is not a truth value: {}",
  + elle::type_info<T>()));
  }
  /*--------------------------.
  