ENH: Update ITK to release branch (v4.8.1 with VS2015 and c++11 fixes)

$ git shortlog slicer-v4.8..2eb422b --no-merges
Abhishek Tiwari (1):
BUG: "tmpImageIndex" not initialized to 0.

Davis Vigneault (2):
DOC: Expanded TreeContainer Example
COMP: Warnings in itkVTKImageExport when compiling with c++11

Hyun Jae Kang (1):
BUG: Fix HDF5 CMake configuration with VS2015

Jean-Christophe Fillion-Robin (2):
COMP: Fix Slicer MacOSX extension packaging setting CMP0042 policy to OLD
COMP: Set policy CMP0042 only if CMake version support it.

Matthew McCormick (12):
BUG: Implement UpdateLargestPossibleRegion for ImageToVTKImageFilter.
BUG: Initialize mutex for 32 bit AtomicInt.
COMP: Disable the gold linker for static builds on Ubuntu 14.04.
BUG: Build BridgeNumPy with Visual Studio.
BUG: Support Python 3 wrapping module initialization.
BUG: Update itkTemplate.py for Python 3.
BUG: Update itkExtras.py for Python 3.
BUG: Prevent Python callback addition recursion.
BUG: Fix test scripts for Python 3.
BUG: Replace GCCXML with CABLE_CONFIGURATION.
COMP: Do not use C++11 alignas in itkAlignedTypedef.
ENH: Bump CMakeLists.txt version to 4.8.1.

Michka Popoff (1):
ENH: Do not link against specific Python library on OS X

Shawn Waldon (1):
COMP: Set target OS X version in environment for tools using compiler

Tobias Wood (2):
BUG: LBFGSB was printing messages even with debug switched off.
BUG: Removed an unguarded print statement.

Vladimir S. FONOV (2):
BUG: Missing ITKIOMINC_EXPORT on __Private()
COMP: Changing the order of HDF5 library components

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24653 3bd1e089-480b-0410-8dfb-8563597acbee