ENH: Removal of VTK 4 Backwards Compatibility Superclasses.

Removed vtkSource, vtkProcessObject and subclasses.
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Overview#Removal_of_VTK_4_Backwards_Compatibility_Superclasses
http://www.vtk.org/Wiki/VTK/Tutorials/New_Pipeline#Converting_an_Existing_Filter_to_the_New_Pipeline

Removed ExecuteInformation().
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Removal_of_Execute.
ENH: VTK6 migration, removal of deprecated Macro.

The following two macros were deprecated in VTK 5.0 that were still supported, but have now been eliminated:
vtkTypeRevisionMacro has been replaced with vtkTypeMacro; vtkCxxRevisionMacro has been removed.
http://www.visitusers.org/index.php?title=VTK_6.0_Upgrade
ENH: VTK6 migration, replacement of SetInput().

Replacement of SetInput() with SetInputData() and SetInputConnection().
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Replacement_of_SetInput.
ENH: VTK6 migration, changes to scalars and extent manipulation.

Changes to Scalars Manipulation Functions.
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Changes_to_Scalars_Manipulation_Functions.
http://vtk.org/Wiki/VTK/VTK6/Migration/WikiExamples#Improve.

Removal of SetWholeExtent and update extent methods
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Removal_of_SetWholeExtent
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Removal_of_Methods_for_Manipulating_Update_Extent