Renamed include/osg/OperationsThread to OperationThread.

Created a new GraphicsThread subclass from OperationThread which allows the
GraphicsContext specific calls to be moved out of the base OperationThread class.

Updated the rest of the OSG to respect these changes.

include/osg/GraphicsThread

@@ -14,10 +14,20 @@
 #ifndef OSG_GRAPHICSTHREAD
 #define OSG_GRAPHICSTHREAD 1
 
-#include <osg/OperationsThread>
+#include <osg/OperationThread>
 
 namespace osg {
 
+class OSG_EXPORT GraphicsThread : public osg::OperationThread
+{
+    public:
+    
+        GraphicsThread();
+        
+        /** Run does the graphics thread run loop.*/        
+        virtual void run();
+};
+
 /** SwapBufferOperation calls swap buffers on the GraphicsContext.*/
 struct OSG_EXPORT SwapBuffersOperation : public Operation
 {