Put back the cxx file for vtkImageStencilIterator.

It turns out that this is necessary for explicit template instantiation
on Windows.  Without it, there are link errors for shared builds.

Imaging/Core/CMakeLists.txt

@@ -26,7 +26,7 @@ set(Module_SRCS
   vtkImageResliceToColors.cxx
   vtkImageShiftScale.cxx
   vtkImageShrink3D.cxx
-  vtkImageStencilIterator.h
+  vtkImageStencilIterator.cxx
   vtkImageThreshold.cxx
   vtkImageTranslateExtent.cxx
   vtkImageWrapPad.cxx

Imaging/Core/vtkImageStencilIterator.cxx

+/*=========================================================================
+
+  Program:   Visualization Toolkit
+  Module:    vtkImageStencilIterator.cxx
+
+  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
+  All rights reserved.
+  See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
+
+     This software is distributed WITHOUT ANY WARRANTY; without even
+     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+     PURPOSE.  See the above copyright notice for more information.
+
+=========================================================================*/
+
+#include "vtkImageStencilIterator.h"
+
+#ifndef VTK_NO_EXPLICIT_TEMPLATE_INSTANTIATION
+
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<signed char>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<char>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<int>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<long>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<short>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<float>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<double>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<unsigned long>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<unsigned short>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<unsigned char>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<unsigned int>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<long long>;
+template class VTKIMAGINGCORE_EXPORT vtkImageStencilIterator<unsigned long long>;
+
+#endif