Added assigned of the InteractiveImageHandler as a cull callback to enable the interactive image to know when it's being actively used as part of rendering a frame.
Refactored the idle mechanism to fix problems with the vnc thread going idle when it shouldn't have.
From David Fries, "This updates the CMakeLists.txt instructions for the commands
to make the doxygen documentation."
From Pawel Ksiezopolski, Added example of using osg::TextureBuffer + GLSL to render forest.
Added repolation of the _deadparts stack which would otherwise been invalidatd by the depth sort of particles.