ENH: VTK6 migration, changes to scalars manipulation functions.

changes to scalars manipulation functions.
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Changes_to_Scalars_Manipulation_Functions.
removal of update() from vtkDataObject.
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Removal_of_Update.