message: core: fix MSVC compiler error
  Somehow, on one machine these changes were needed in order to avoid
  MSVC complaining about:
  warning C4346: 'iterator': dependent name is not a type
diff: @@ -24,11 +24,11 @@ public:
  }
  using iterator = typename std::deque<std::shared_ptr<T>>::iterator;
  - LockedQueue<T>::iterator begin() { return _queue.begin(); }
  + iterator begin() { return _queue.begin(); }
  - LockedQueue<T>::iterator end() { return _queue.end(); }
  + iterator end() { return _queue.end(); }
  - LockedQueue<T>::iterator erase(LockedQueue<T>::iterator it) { return _queue.erase(it); }
  + iterator erase(iterator it) { return _queue.erase(it); }
  class Guard {
  public:
  