Update CMakeLists.txt

Disable CUDA on OS X Mavericks (== Darwin 13), because it is not supported there.

See http://answers.ros.org/question/94771/building-ros-on-osx-109-solution/?answer=101176#post-id-101176

This PR only serves as a reference and for hosting the patch (to be applied manually). The patch should be included in https://github.com/ros-gbp/opencv2-release/tree/patches/release/hydro/opencv2 and possibly also groovy (which I haven't tried).