Added support for AbortRendering flag pointer in osg::State which is used

by osgUtil::RenderLeaf to test if any abort state has been set, if so it
doesn't do any further drawing.

The osgProducer::Viewer has been set up to set the osg::State's it manages
with their AbortRendering flag pointers set to the osgProducer::Viewer::_done
memeber varaible.  Now when escape is pressed the rendering is aborted early.

src/osgProducer/KeyboardMouseCallback.cpp

@@ -26,6 +26,11 @@ void KeyboardMouseCallback::keyPress( Producer::KeySymbol key )
 #endif
     }
     
+    if (_done)
+    {
+        // need to contact the viewer so pass on the abort..
+    }
+    
     osg::ref_ptr<EventAdapter> event = new EventAdapter;
     event->adaptKeyPress(getTime(),key);