COMP: CommandIterationUpdate has field whose type uses anonymous namespace.

For the warning:

  /scratch/dashboards/Linux-x86_64-gcc4.1/ITK/Examples/Registration/ImageRegistrationHistogramPlotter.cxx:391:
  warning: 'CommandIterationUpdate' has a field
  'CommandIterationUpdate::m_JointHistogramWriter' whose type uses the
  anonymous namespace

Change-Id: I63adee3894104d6d755477357526fa25e29bb6c0
Merge topic 'HistogramPlotter-cxx'

31dd0d8d COMP: CommandIterationUpdate has field whose type uses anonymous namespace.