Extend the concept to operator-> and fix the bug in edge_circulator.

The work-around is a little fishy, because it involves storing the
segment, but so it be. The concept shouldn't check for operator->
though, it is too strict.

Circulator/include/CGAL/Circulator/Circulator_concepts.h

@@ -11,6 +11,16 @@
 
 namespace CGAL { namespace Concepts {
 
+template <typename T>
+void deref(T& t) {
+  t.operator->();
+}
+
+template <typename T>
+void deref(T*) {
+  // valid anyway
+}
+
 // N.B.: there is no such concept as Circulator as it is immaterial
 template <typename C>
 struct ForwardCirculator 
@@ -40,6 +50,8 @@ struct ForwardCirculator
     a++;
     (void)*a; // suppress unused warning, don't check the return type
               // to allow for proxies
+
+    deref(a);
   }
 private:
   C a;
@@ -90,6 +102,3 @@ private:
 
 
 #endif /* CGAL_CIRCULATOR_CONCEPTS_H */
-
-
-

Polygon/include/CGAL/Polygon_2/Polygon_2_edge_circulator.h

@@ -55,6 +55,8 @@ class Polygon_2_const_edge_circulator {
 
   private:
     Vertex_const_circulator first_vertex;
+    // carry around the segment to be a proper iterator
+    Segment_2               segment;
 
   public:
     Polygon_2_const_edge_circulator() {}
@@ -86,13 +88,20 @@ class Polygon_2_const_edge_circulator {
       return !(first_vertex == x.first_vertex);
     }
 
-    Segment_2 operator*() const
+    const Segment_2& operator*() const
     {
       Vertex_const_circulator second_vertex = first_vertex;
       ++second_vertex;
       typename Traits::Construct_segment_2 construct_segment_2 = 
             Traits().construct_segment_2_object();
-      return construct_segment_2(*first_vertex, *second_vertex);
+      const_cast<Polygon_2_const_edge_circulator*>(this)->segment = 
+          construct_segment_2(*first_vertex, *second_vertex);
+      return segment;
+    }
+
+    const Segment_2* operator->() const 
+    {
+      return &(**this);
     }
 
     Polygon_2_const_edge_circulator<_Traits, _Container>& operator++()