ENH: VTK6 migration, removal of VTK 4 Backwards Compatibility Superclasses.

Removal of VTK 4 Backwards Compatibility Superclasses.
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
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Overview#Removal_of_Data_Objects.E2.80.99_Dependency_on_the_Pipeline
ENH: VTK6 migration, removal of Execute, vtkType deprecations.

1) vtkType deprecations
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/vtkType_deprecations
2) Removal of Execute
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Removal_of_Execute
ENH: VTK6 migration, removal of SetWholeExtent and update extent methods.

1) Removal of SetWholeExtent() from vtkDataObject
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Removal_of_SetWholeExtent
2) WIP: Removal of Methods for Manipulating Update Extent
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Removal_of_Methods_for_Manipulating_Update_Extent
ENH: VTK6 migration, change to AllocateOutputData.

Change to AllocateOutputData() in vtkImageAlgorithm.
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Change_to_AllocateOutputData