insert_any_extra_boundary_points contiguously

This fixes Triangle unit tests on distributed meshes for me.

... which means we really ought to be finding whatever it is in our
Triangle interface that doesn't support non-contiguous node numbering,
but I couldn't find it on a quick glance, so "don't trigger the bug in
my other code" is the best I can do right now.

Author: roystgnr

src/mesh/triangulator_interface.C

@@ -170,6 +170,10 @@ void TriangulatorInterface::insert_any_extra_boundary_points()
   const int n_interpolated = this->get_interpolate_boundary_points();
   if ((_triangulation_type==PSLG) && n_interpolated)
     {
+      // If we were lucky enough to start with contiguous node ids,
+      // let's keep them that way.
+      dof_id_type nn = _mesh.max_node_id();
+
       std::vector<std::pair<unsigned int, unsigned int>> old_segments =
         std::move(this->segments);
 
@@ -195,7 +199,7 @@ void TriangulatorInterface::insert_any_extra_boundary_points()
                 ((n_interpolated-i) * *(Point *)(begin_node) +
                  (i+1) * *(Point *)(end_node)) /
                 (n_interpolated + 1);
-              Node * next_node = _mesh.add_point(new_point);
+              Node * next_node = _mesh.add_point(new_point, nn++);
               this->segments.emplace_back(current_id,
                                           next_node->id());
               current_id = next_node->id();