be individually turned on or off. Moved the OpenFlight code across to use the
new scheme, removing the old hack of using node masks to achieve the same end
result.
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.
