message: Fix unused variable warning in current rustc.
diff: @@ -195,12 +195,12 @@ fn graph_map(bench: &mut Bencher)
  fn stable_graph_retain_nodes(bench: &mut Bencher)
  {
  let mut a = parse_stable_graph::<Directed>(BIGGER);
  - bench.iter(|| a.retain_nodes(|gr, i| (i.index() + 1) % 3700 != 0));
  + bench.iter(|| a.retain_nodes(|_gr, i| (i.index() + 1) % 3700 != 0));
  }
  #[bench]
  fn stable_graph_retain_edges(bench: &mut Bencher)
  {
  let mut a = parse_stable_graph::<Directed>(BIGGER);
  - bench.iter(|| a.retain_edges(|gr, i| (i.index() + 1) % 3700 != 0));
  + bench.iter(|| a.retain_edges(|_gr, i| (i.index() + 1) % 3700 != 0));
  }
  