ENH: Bump vtkDICOM version

Recent changes to KWSys removed the vtksys_stl and vtksys_ios
compatibility layers

Remote/vtkDICOM.remote.cmake

@@ -5,6 +5,6 @@
 vtk_fetch_module(vtkDICOM
   "Dicom classes and utilities"
   GIT_REPOSITORY https://github.com/lorensen/vtk-dicom
-  # July 9, 2015 - first working as a vtk remote module
-  GIT_TAG vtkRemote
+  # September 3, 2015 - vtksys changes
+  GIT_TAG f4556b282b1f9e3f3adb98a7ad618b0bb57dc6ab
   )