Added setting colormask to SceneView on every frame to allow toggling

between stereo on and off in Anaglyphic mode.

src/osgUtil/SceneView.cpp

@@ -588,6 +588,9 @@ void SceneView::draw()
     else
     {
         _globalState->setAttribute(_viewport.get());
+        osg::ref_ptr<osg::ColorMask> cmask = osgNew osg::ColorMask;
+        cmask->setMask(true,true,true,true);
+        _globalState->setAttribute(cmask.get());
 
         // bog standard draw.
         drawStage(_renderStage.get());