message: Adds an index() function to slam's OrderedSet iterator
  This returns the index of the currently pointed to element.
diff: @@ -310,6 +310,11 @@ public:
  return OrderedSetIterator<T, true>(this->m_pos, this->m_orderedSet);
  }
  /// \}
  +
  + PositionType index() const
  + {
  + return m_pos;
  + }
  protected:
  /** Implementation of advance() as required by IteratorBase */
  void advance(PositionType n) { m_pos += n * stride(); }
  