UPdates to CullVisitor so that it keeps in sync with the new method paramter

change in osg::Billboard.

Removed in instance of an object being passed () brackets, have removed the
brackets to avoid an amiguity with the compiler intepreting it as a function.

src/osgDB/ReadFile.cpp

@@ -72,7 +72,7 @@ Node* osgDB::readNodeFiles(std::vector<std::string>& commandLine)
     }
     else  // size >1
     {
-        osg::Group* group = new osg::Group();
+        osg::Group* group = new osg::Group;
         for(NodeList::iterator itr=nodeList.begin();
             itr!=nodeList.end();
             ++itr)