Made the more of the OSG's referenced object desctructors protected to ensure

that they arn't created on the stack inappropriately.

Split the implemention of Matrix up so that it is a simple no referenced counted
class and can be safefly created on the stack.  To support referenced counting a
seperate subclass now exists, this is RefMatrix which inherits from both Matrix and
Object.

src/osg/State.cpp

@@ -10,7 +10,7 @@ using namespace osg;
 State::State()
 {
     _contextID = 0;
-    _identity = new osg::Matrix(); // default Matrix constructs to identity.
+    _identity = new osg::RefMatrix(); // default RefMatrix constructs to identity.
     _projection = _identity;
     _modelView = _identity;