on osgUtil by implementing a NodeVisitor::VisitorType enum, and associated
g/setVisitorType. This allows callbacks to querry the visitor/traversal
type without doing down cast's to specific visitor subclasses such as
osgUtil::AppVisitor/CullVisitor.
but getting there.
o First cut of osgcluster demo. Very simple beginings. Alas
I only one PC here so I can't test it in its current guise.
o New support for NodeCallbacks, via AppCallback attached to
osg::Node's, and a default osgUtil::AppVisitor which calls them on
each frame.
o Support for traversal masks in osg::NodeVisitor, osg::Node
which allows nodes to be switched on or off via a bit mask.
o Suppport for traversal number (frame number) and reference time
into osg::NodeVisitor to handle syncronization of app and cull
traversals. This also assist clustering as traversal number
master to slaves.
