Renamed the osg::EarthSky to osg::ClearNode to make it more obvious what

role it has play and make it more relevant to non vis-sim applications.

src/osg/ClearNode.cpp

@@ -0,0 +1,20 @@
+#include <osg/ClearNode>
+
+#include <algorithm>
+
+using namespace osg;
+
+/**
+ * ClearNode constructor.
+ */
+ClearNode::ClearNode()
+{
+    StateSet* stateset = osgNew StateSet;
+    stateset->setRenderBinDetails(-1,"RenderBin");
+    setStateSet(stateset);
+    
+    _requiresClear = true;
+    _clearColor.set(0.0f,0.0f,0.0f,1.0f);  
+
+}
+