Don't normalize path if function is not in Boost
Remove Boost Chrono dependency

* Revert Boost version to 1.40.
* Move io/image* into OpenNI2.
Merge pull request #909 from jspricke/boost_chrono

Support Boost 1.46 (needed for Ubuntu precise)
Add Ensenso support in CMake files
Add Ensenso grabber example
Add EnsensoGrabber class
Add Ensenso simple viewer
Add Ensenso documentation & tutorial