STYLE: Use ITK_NULLPTR to utilize c++11 features

    Where available, use c++11 features to identify
    potential nullptr usage errors.

    python run-clang-tidy.py -clang-tidy-binary ~/software/clang+llvm-3.8.0-x86_64-linux-gnu-ubuntu-14.04/bin/clang-tidy -checks=-*,modernize-use-nullptr -header-filter=/home/grizonnetm/projets/otb/src/OTB/Modules/.*/.*/include/.* -j8 -fix -p ~/projets/otb/bin/release/OTB-clang3.8/ ~/projets/otb/src/OTB/Modules/*/*/src/*.cxx ~/projets/otb/src/OTB/Modules/*/*/app/*.cxx ~/projets/otb/src/OTB/Examples/*/*.cxx ~/projets/otb/src/OTB/Modules/*/*/test/*.cxx > ~/temporary/run-clang-tidy-nullptr-log.txt

    find . -type f -print -name "*.h" -o -name "*.txx" -o -name "*.cxx" |xargs perl -pi -e 's/nullptr/ITK_NULLPTR/g'