BUG: Extension packaging: Ensure @rpath is not applied at build time

Having the ids of library set as full path is mandatory to ensure
fixup bundle script works properly.

Setting CMAKE_MACOSX_RPATH to 0 ensures that @rpath will not be automatically
be applied to extension module libraries where the CMake minimum required
version >= 3.0.

CMake 3.0 is the version where CMP0042 is set to NEW by default.

CMP0042 set to NEW means that CMAKE_MACOSX_RPATH is ON by default.

Notes: Existing workarounds within Slicer core (e.g use of patched version
of ITK forcing CMP0042 to OLD) will be removed and a similar change will
also be applied to SlicerCPack.cmake.

See SBU-BMI/SlicerOpenCV#30

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25180 3bd1e089-480b-0410-8dfb-8563597acbee