Fix find_package(PythonLibs ...)

The version should be passed as argument, not by setting PythonLibs_FIND_VERSION.

This breaks builds in recentely released cmake 3.0.0 it seems: http://answers.ros.org/question/178375/linking-camera_info_manager-fails-on-osx/

This change should also be backported to groovy/hydro.
Merge pull request #42 from NikolausDemmel/patch-1

Fix find_package(PythonLibs ...)