fix crash and warn about experimental nature of this algo

Mesh/meshPartition.cpp

@@ -184,6 +184,7 @@ int PartitionMeshFace(std::list<GFace*> &cFaces, meshPartitionOptions &options)
 
 int RenumberMeshElements(std::vector<MElement*> &elements, meshPartitionOptions &options)
 {
+  Msg::Warning("Mesh renumbering is still experimental...");
   if (elements.size() < 3) return 1;
   GModel *tmp_model = new GModel();
   std::set<MVertex *> setv;
@@ -220,6 +221,8 @@ int RenumberMeshElements(std::vector<MElement*> &elements, meshPartitionOptions
         gr->pyramids.push_back((MPyramid*)(*it));
     }
     tmp_model->add(gr);
+    RenumberMesh(tmp_model, options, elements);
+    tmp_model->remove(gr);
   }
   delete tmp_model;
   return 1;