VS2013: Adjust cppunit to 12.0 vcproj version

Change-Id: I9223fc0620bf31389ab4ea0971835dd7a27feb7e
Reviewed-on: https://gerrit.libreoffice.org/10159
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>