New reverse_graph_edge_descriptor type missing operators

[justin.viiret@…]

We noticed on upgrading the version of Boost we use to 1.48 that the changes in reverse_graph.hpp broke our ability to construct an STL set of reverse graph edge descriptors.

I think this is likely related to changeset [73997], where the reverse_graph_edge_descriptor class was added; it has equals and not-equals operators, but no less-than.

Adding "operator<" for the type seems to be enough to allow sets of reverse edge descriptors, but adding the same set of operators available for the underlying edge_descriptor might be warranted..?

@@ -36,6 +36,9 @@
       friend bool operator==(const reverse_graph_edge_descriptor& a, const reverse_graph_edge_descriptor& b) {
         return a.underlying_desc == b.underlying_desc;
       }
+      friend bool operator<(const reverse_graph_edge_descriptor& a, const reverse_graph_edge_descriptor& b) {
+        return a.underlying_desc < b.underlying_desc;
+      }
       friend bool operator!=(const reverse_graph_edge_descriptor& a, const reverse_graph_edge_descriptor& b) {
         return a.underlying_desc != b.underlying_desc;
       }

[Jeremiah Willcock]

(In [75547]) Added comparison operators; fixes #6137