COMP: C++11 conformance for static initialization

error: non-constant-expression cannot be narrowed from type 'unsigned long' to 'IndexValueType' (aka 'long') in initializer list [-Wc++11-narrowing]
as identifiied by the clang compiler.

From: Hans Johnson <hans-johnson@uiowa.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22913 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: C++11 compiler warning convert NULL to bool

warning: implicit conversion of NULL constant to 'bool' [-Wnull-conversion]

From: Hans Johnson <hans-johnson@uiowa.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22914 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: C++11 convertsion of types

error: no viable conversion from 'DiffusionTensor3DExtended<float>' to 'DiffusionTensor3DExtended<double>'

By preferring initialization to assignment this error is avoided.

From: Hans Johnson <hans-johnson@uiowa.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22915 3bd1e089-480b-0410-8dfb-8563597acbee