[vtkusers] create a polyData from selected cell

[David Doria]

 vtkSmartPointer<vtkPolyData> newdata =
   vtkSmartPointer<vtkPolyData>::New();
vtkPoints* cellPoints = selected->GetPoints();
newdata->SetPoints(cellPoints);

vtkSmartPointer< vtkTriangleFilter > triangleFilter =
  vtkSmartPointer<vtkTriangleFilter>::New();
triangleFilter->SetInputConnection(newdata->GetProducerPort());
triangleFilter->Update();

vtkSmartPointer< vtkLoopSubdivisionFilter > subdivisionFilter =
  vtkSmartPointer<vtkLoopSubdivisionFilter>::New();
subdivisionFilter->SetNumberOfSubdivisions(numberOfSubdivisions);
subdivisionFilter->SetInputConnection(triangleFilter->GetOutputPort());
subdivisionFilter->Update();