Use standard dcmtk snapshot for building.

After discussion at CTK hackfest, decision was taken to keep
CTK's default version of the upstream libraries at published
releases wherever possible.  Applications (slicer, mitk, maf, etc)
can use the DCMTK_DIR setting to specify a newer version if
needed and provide tested backwards compatible patches if there
are fixes needed to work with newer versions.

CMakeExternals/DCMTK.cmake

@@ -23,7 +23,7 @@ if(${add_project})
   if(CTK_SUPERBUILD)
 
     if(NOT DEFINED DCMTK_DIR)
-      set(revision_tag ab844899a92f46e2d880c38c85ce098933533aef)
+      set(revision_tag ae3b946f6e6231)
       if(${proj}_REVISION_TAG)
         set(revision_tag ${${proj}_REVISION_TAG})
       endif()