Added osg::State::popAllStateSets() method to pop all remain StateSet's off

the state stack, thus readying the state object to recieve a new frame.

Removed the state.reset() call in osgUtil::SceneView::cull() as this was
causing problems with stats producing inheritance of state when toggling
stats on.

src/osg/State.cpp

@@ -148,6 +148,11 @@ void State::pushStateSet(const StateSet* dstate)
     }
 }
 
+void State::popAllStateSets()
+{
+    while (!_drawStateStack.empty()) popStateSet();
+}
+
 void State::popStateSet()
 {
     if (_drawStateStack.empty()) return;