Change Terrain so that it subclassed from CoordinateSystemNode.

Implemented new update scheme of GeometryTechnique to avoid potential threading issues.

Added Terrain support to .ive.

src/osgPlugins/ive/DataInputStream.cpp

@@ -112,6 +112,7 @@
 
 #include "Text.h"
 
+#include "Terrain.h"
 #include "TerrainTile.h"
 #include "Locator.h"
 #include "ImageLayer.h"
@@ -1836,6 +1837,10 @@ osg::Node* DataInputStream::readNode()
         node = new osgTerrain::TerrainTile();
         ((ive::TerrainTile*)(node.get()))->read(this);
     }
+    else if(nodeTypeID== IVETERRAIN){
+        node = new osgTerrain::Terrain();
+        ((ive::Terrain*)(node.get()))->read(this);
+    }
     else if(nodeTypeID== IVEVOLUME){
         node = new osgVolume::Volume();
         ((ive::Volume*)(node.get()))->read(this);