graph/labeled_graph: added remove_labeled_vertex

I took this patch from this ticket:
https://svn.boost.org/trac/boost/ticket/9493

include/boost/graph/labeled_graph.hpp

@@ -260,6 +260,19 @@ namespace graph_detail
     }
     //@}
 
+    /** @name Remove Labeled Vertex */
+    //@{
+    template <typename Container, typename Label, typename Graph>
+    void remove_labeled_vertex(Container& c, Graph& g, Label const& l)
+    {
+      typename Container::iterator c_it = c.find(l);
+      if (c_it != c.end()) {
+        boost::remove_vertex(c_it->second, g);
+        c.erase(c_it);
+      }
+    }
+    //@}
+
 } // namespace detail
 
 struct labeled_graph_class_tag
@@ -451,7 +464,7 @@ class labeled_graph : protected labeled_graph_types< Graph, Label, Selector >
     /** Remove the vertex with the given label. */
     void remove_vertex(Label const& l)
     {
-        return boost::remove_vertex(vertex(l), _graph);
+        return graph_detail::remove_labeled_vertex(_map, _graph, l);
     }
 
     /** Return a descriptor for the given label. */