o Updated Metrowerks files for MacOS. They aren't 100% there yet,

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.

src/osg/Viewport.cpp

@@ -0,0 +1,22 @@
+#include <osg/Viewport>
+
+using namespace osg;
+
+Viewport::Viewport()
+{
+    _x = 0;
+    _y = 0;
+    _width = 800;
+    _height = 600;
+}
+
+
+Viewport::~Viewport()
+{
+}
+
+void Viewport::apply(State&) const
+{
+    glViewport(_x,_y,_width,_height);
+}
+