COMP: Build 'DICOMDiffusionVolumePlugin' only if diffusion support is enabled

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22863 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Add convenience function 'slicer.util.getFirstNodeByClassAndName'

This is required because the function vtkMRMLScene::GetFirstNode
is not wrapped. Indeed, his third parameter is a pointer to
an integer.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22864 3bd1e089-480b-0410-8dfb-8563597acbee