Fix issues when building on systems with libc++ (OS X 10.9 Mavericks)

These changes enable building on systems that use libc++ as the c++ standard library implementation, currently the most prominent being Mac OS X 10.9 Mavericks. Basically there are some trivial namespace issues that can be easily adapted. This should fix #52 and address the some of the issues discussed here: http://answers.ros.org/question/94771/building-octomap-orocos_kdl-and-other-packages-on-osx-109-solution/