Added shader based transfer function, enabled via --gpu-tf
Added shader based transfer function, enabled via --gpu-tf


marchelbling/osg,scrawl/osg,marchelbling/osg,scrawl/osg,artoolkit/osg,scrawl/osg,artoolkit/osg,artoolkit/osg,jtorresfabra/osg,marchelbling/osg,artoolkit/osg,tomasthoresen/osg,marchelbling/osg,tomasthoresen/osg,openscenegraph/osg,scrawl/osg,jtorresfabra/osg,openscenegraph/osg,openscenegraph/osg,jtorresfabra/osg,jtorresfabra/osg,tomasthoresen/osg,openscenegraph/osg,tomasthoresen/osg