ENH: VTK6 migration, removal of manipulating update extent.

Removal of Methods for Manipulating Update Extent.
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Removal_of_Methods_for_Manipulating_Update_Extent.
http://vtk.org/Wiki/VTK/VTK6/Migration/WikiExamples#Improve.