BUG: Update VTK to revert changes associated with vtkColorTransferFunction

It turns out the proposed fix (http://review.source.kitware.com/#/c/19012/)
does not completely address the problem. This commit revert it and also
revert the VTK commit kitware/VTK@238163f (6657: Add out-of-range colors
to color maps) as it was done in r23910.

The following tests are now passing (tested on Ubuntu 14.04):

 py_sceneImport2428
 py_ThresholdThreadingTest
 py_StandaloneEditorWidgetTest
 py_RSNAVisTutorial
 py_RSNAQuantTutorial
 py_RSNA2012ProstateDemo
 py_JRC2013Vis
 py_NeurosurgicalPlanningTutorialMarkupsSelfTest
 py_NeurosurgicalPlanningTutorial

$ git shortlog e0dda5f..c9fd5fb
Jean-Christophe Fillion-Robin (2):
Revert "Fix crash where vtkColorTransferFunction has 0 nodes"
Revert "6657: Add out-of-range colors to color maps"

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23983 3bd1e089-480b-0410-8dfb-8563597acbee