Issue #2642

Example of performance on a MacBookPro laptop:
AddData (BrainAtlas2012.mrb) took 39877 msecs
CloseScene () took 26271 msecs
CloseScene () took 136 msecs
AddData (BrainAtlas2012.mrb) took 36945 msecs
ModifyNode (vtkMRMLScalarVolumeNode1) took 4 msecs
ModifyNode (vtkMRMLScalarVolumeNode2) took 28 msecs
ModifyNode (vtkMRMLScalarVolumeNode3) took 16 msecs
ModifyNode (vtkMRMLModelHierarchyNode2) took 13 msecs
ModifyNode (vtkMRMLModelNode5) took 1 msecs
ModifyNode (vtkMRMLModelNode4) took 0 msecs
ModifyNode (vtkMRMLModelDisplayNode5) took 12 msecs
ModifyNode (vtkMRMLModelHierarchyNode3) took 12 msecs
ModifyNode (vtkMRMLModelStorageNode1) took 4 msecs
ModifyNode (vtkMRMLModelHierarchyNode301) took 17 msecs
ModifyNode (vtkMRMLModelDisplayNode304) took 21 msecs
ModifyNode (vtkMRMLModelHierarchyNode302) took 17 msecs
AddNode (vtkMRMLModelNode5) took 90 msecs
AddNode (vtkMRMLModelNode302) took 45 msecs

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21580 3bd1e089-480b-0410-8dfb-8563597acbee