ENH: Update ITK to v4.8

$ git shortlog 5f95aa6..3388d7b --no-merges
Bradley Lowekamp (4):
BUG: Remove reliance on exceptions in StringTools::ToData methods
BUG: Remove reliance on exceptions in StringTools::ToData methods
BUG: Fix WriteCellsAsBinary and valgrind defects
COMP: Explicitly export SingleValuedNonLinearVnlOptimizerv4

Davis Vigneault (1):
COMP: C++11 Warnings in thirdparty PNG module.

Matthew McCormick (13):
COMP: Address may bu used uninitialized in IdentityTransformTest.
COMP: Address array subscript above bounds in VTKPolyDataReader.
COMP: Work around GDCM test segfault with Clang 3.5+.
BUG: Do not use pthreads with Emscripten.
COMP: Fix unused parameter warnings in itkMultiThreaderNoThreads.
BUG: Do not output CMake log files in itkSystemInformationTest.
COMP: Work around segfaults with VS12 in RegionOfInterestImageFilter.
DOC: Update Wiki Examples Remote to June 26, 2015.
COMP: Update ParabolicMorphology to address doxygen warning.
COMP: Add missing exports in the ITKFEM module.
BUG: Use CMAKE_LIBRARY_OUTPUT_DIRECTORY for build tree WrapITK.pth.
DOC: Document grafting the input image in composite filters.
DOC: Bump SphinxExample remote module version to 2015-07-02.

Michka Popoff (1):
ENH: Update PyInit for Python 3

From: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24404 3bd1e089-480b-0410-8dfb-8563597acbee