From Xin Li, "use std::list::splice to replace std::list::insert and std::list::clear

it may use the constant time to move all the items in the '_eventQueue' to 'events', and reduce the mutex holding time"

src/osgGA/EventQueue.cpp

@@ -53,8 +53,7 @@ bool EventQueue::takeEvents(Events& events)
     OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_eventQueueMutex);
     if (!_eventQueue.empty())
     {
-        events.insert(events.end(),_eventQueue.begin(),_eventQueue.end());
-        _eventQueue.clear();
+        events.splice(events.end(), _eventQueue);
         return true;
     }
     else