Cleaned up osgTerrain, renaming the Terrain and Renderer class to

HeightFieldNode and HeightFieldRender to better reflect their function.
Removed the GeoMipMapRenderer.cpp stub as the implemention will be left
to a plugin.  Added Version functions.

src/osgTerrain/Version.cpp

@@ -0,0 +1,12 @@
+#include <osgTerrain/Version>
+
+const char* osgTerrainGetVersion()
+{
+    return "0.9.6";
+}
+
+
+const char* osgTerrainGetLibraryName()
+{
+    return "Open Scene Graph Terrain Library";
+}