message: Fix compilation for rust nightly
  Fixes by removing ambiguity between Ord::max and IndexType::max in two locations.
diff: @@ -486,7 +486,7 @@ impl<N, E, Ty, Ix> Graph<N, E, Ty, Ix>
  let node = Node{weight: weight, next: [EdgeIndex::end(), EdgeIndex::end()]};
  let node_idx = NodeIndex::new(self.nodes.len());
  // check for max capacity, except if we use usize
  - assert!(Ix::max().index() == !0 || NodeIndex::end() != node_idx);
  + assert!(<Ix as IndexType>::max().index() == !0 || NodeIndex::end() != node_idx);
  self.nodes.push(node);
  node_idx
  }
  @@ -523,7 +523,7 @@ impl<N, E, Ty, Ix> Graph<N, E, Ty, Ix>
  pub fn add_edge(&mut self, a: NodeIndex<Ix>, b: NodeIndex<Ix>, weight: E) -> EdgeIndex<Ix>
  {
  let edge_idx = EdgeIndex::new(self.edges.len());
  - assert!(Ix::max().index() == !0 || EdgeIndex::end() != edge_idx);
  + assert!(<Ix as IndexType>::max().index() == !0 || EdgeIndex::end() != edge_idx);
  let mut edge = Edge {
  weight: weight,
  node: [a, b],
  