COMP: Fix ResampleDTIVolume build error on macosx

This commit fixes a build error happening without ITKV3_COMPATIBILITY
enabled. To address the error message reported below, the module now uses
the concrete class VersorRigid3DTransform instead of the base class
Rigid3DTransform.

//-----------
In file included from /path/to/Slicer/Modules/CLI/ResampleDTIVolume/ResampleDTIVolume.cxx:16:
In file included from /path/to/Slicer/Modules/CLI/ResampleDTIVolume/itkDiffusionTensor3DRigidTransform.h:68:
/path/to/Slicer/Modules/CLI/ResampleDTIVolume/itkDiffusionTensor3DRigidTransform.txx:53:42: error: no viable conversion from 'Pointer' (aka 'SmartPointer') to 'typename Rigid3DTransformType::Pointer' (aka 'SmartPointer')
typename Rigid3DTransformType::Pointer rigidTransform = Rigid3DTransformType::New();
^ ~~~~~~~
/path/to/Slicer-build/ITKv4/Modules/Core/Common/include/itkSmartPointer.h:65:3: note: candidate constructor not viable: no known conversion from 'Pointer' (aka 'SmartPointer') to 'const SmartPointer &' for 1st argument;
SmartPointer (const SmartPointer< ObjectType > & p):
^
/path/to/Slicer-build/ITKv4/Modules/Core/Common/include/itkSmartPointer.h:70:3: note: candidate constructor not viable: no known conversion from 'Pointer' (aka 'SmartPointer') to 'ObjectType ' (aka 'itk::Rigid3DTransform ') for 1st argument;
SmartPointer (ObjectType p):
^
/path/to/Slicer-build/ITKv4/Modules/Core/Common/include/itkSmartPointer.h:86:3: note: candidate function
operator ObjectType () const
^
1 error generated.
//-----------

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23962 3bd1e089-480b-0410-8dfb-8563597acbee