Added DataVariance enum and set/get fields to osg::Object to help identify

which objects have values that vary over the lifetime of the object (DYNAMIC)
and ones that do not vary (STATIC).  Removed the equivalent code in
osg::Transform, StateSet and StateAttribute, as these are now encompassed
by the new DataVariance field.

Removed MatrixMode enum from Matrix, and associated fields/parameters from
osg::Transfrom and osg::NodeVisitor, since MatrixMode was not providing
any useful functionality, but made the interface more complex (MatrixMode
was an experimental API)

Added ReferenceFrame field to osg::Transform which allows users to specify
transforms that are relative to their parents (the default, and previous behavior)
or absolute reference frame, which can be used for HUD's, camera relative
light sources etc etc.  Note, the view frustum culling for absolute Transform
are disabled, and all their parents up to the root are also automatically
have view frustum culling disabled.  However, once passed an absolute Transform
node culling will return to its default state of on, so you can still cull
underneath an absolute transform, its only the culling above which is disabled.

include/osg/Object

@@ -34,7 +34,7 @@ class SG_EXPORT Object : public Referenced
             and therefore cannot be constructed on its own, only derived
             classes which override the clone and className methods are
             concrete classes and can be constructed.*/
-        Object() {}
+        inline Object():Referenced(),_dataVariance(DYNAMIC) {}
 
         /** Copy constructor, optional CopyOp object can be used to control
           * shallow vs deep copying of dynamic data.*/
@@ -53,6 +53,23 @@ class SG_EXPORT Object : public Referenced
         /** return the name of the object's class type. Must be defined
             by derived classes.*/
         virtual const char* className() const = 0;
+        
+
+        enum DataVariance
+        {
+            DYNAMIC,
+            STATIC
+        };
+        
+        /** Set the data variance of this object.
+           * Can be set to either STATIC for values that do not change over the lifetime of the object,
+           * or DYNAMIC for values that vary over the lifetime of the object. The DataVariance value
+           * can be used be routines such as optimzation codes that wish to share static data.*/
+        inline void setDataVariance(const DataVariance dv) { _dataVariance = dv; }
+
+        /** Get the data variance of this object.*/
+        inline const DataVariance getDataVariance() const { return _dataVariance; }
+
 
     protected:
 
@@ -64,6 +81,8 @@ class SG_EXPORT Object : public Referenced
             forcing all nodes to be created on the heap i.e Node* node
             = new Node().*/
         virtual ~Object() {}
+        
+         DataVariance _dataVariance;
 
     private: