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.

Change-Id: If8b93aa0cf30aa0fd0dcddc75f1453fa667230de
Merge branch 'BaditkNamespaceSpecification' into release
Merge branch 'release'