COMP: Update ITKv4 to fix DTIAtlasBuilder visual studio build errors.

It includes commit 69e6bc:

COMP: VectorIndexSelectionCastImageFilter extra itk namespace.
The itk:: namespace specification should not be given within
namespace itk{ } -- it is against ITK style and confuses some
compilers.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21754 3bd1e089-480b-0410-8dfb-8563597acbee