OSX Path Additions

I personally don't use homebrew, so my libfreenect gets installed in to /usr/local instead of /usr by the cmake install target. I fixed this by adding the right include and library paths to the the Freenect driver makefile.

It's also worth noting that if you install libfreenect with cmake built from source, then you have to build it as a universal binary or OpenNI won't link. You can do this by setting `CMAKE_OSX_ARCHITECTURES=i386;x86_64` when running ccmake.

After that, I can confirm that the samples work, although I've been unable to correctly get an Xcode project set up to create my own openni-based application.