Added support for the managing the StateSet above a LightSource node,

and made it an osg::Group so that it can be used a decorator above a
scene.

Added osgclip demo to the test suite.

src/osg/LightSource.cpp

@@ -6,6 +6,9 @@ LightSource::LightSource()
 {
     // switch off culling of light source nodes by default.
     setCullingActive(false);
+    _dstate = osgNew StateSet;
+    _value = StateAttribute::ON;
+    _light = osgNew Light;
 }
 
 
@@ -14,6 +17,29 @@ LightSource::~LightSource()
     // ref_ptr<> automactially decrements the reference count of attached lights.
 }
 
+
+void LightSource::setLight(Light* light)
+{
+    _light = light;
+    setLocalStateSetModes(_value);
+}
+
+// Set the GLModes on StateSet associated with the ClipPlanes.
+void LightSource::setStateSetModes(StateSet& stateset,const StateAttribute::GLModeValue value) const
+{
+    if (_light.valid())
+    {
+        _light->setStateSetModes(stateset,value);
+    }
+}
+
+void LightSource::setLocalStateSetModes(const StateAttribute::GLModeValue value)
+{
+    if (!_dstate) _dstate = osgNew StateSet;
+    _dstate->setAllToInherit();
+    setStateSetModes(*_dstate,value);
+}
+
 const bool LightSource::computeBound() const
 {
     // note, don't do anything right now as the light itself is not