Changed the Node::ParentList to be a list of osg::Node rather than osg::Group, and added addChild, removeChild, replaceChild virtual method to Node to enable code

to user code compile with minimal modifications to account for the new change to the Node ParentList.

src/osg/Node.cpp

@@ -93,14 +93,14 @@ Node::~Node()
     setStateSet(0);
 }
 
-void Node::addParent(osg::Group* node)
+void Node::addParent(osg::Node* node)
 {
     OpenThreads::ScopedPointerLock<OpenThreads::Mutex> lock(getRefMutex());
 
     _parents.push_back(node);
 }
 
-void Node::removeParent(osg::Group* node)
+void Node::removeParent(osg::Node* node)
 {
     OpenThreads::ScopedPointerLock<OpenThreads::Mutex> lock(getRefMutex());