code: void mergeCalls(CallTracker rhs)
      {
          synchronized (this._associatedChannels)
          {
              this._associatedChannels.addAll(rhs._associatedChannels);
              // not certain this is necessary but lets just tidy up a bit.
              rhs._associatedChannels.clear();
          }
      }
docs: Used to merge two calls into a single call. This is required as during a
  masquerade a new channel is created an initially we will create a
  CallTracker for it. When the masquerade event finally turns up we will
  realise it belongs to an existing CallTracker and as such we need to
  merge the two CallTrackers.
  
  @param rhs