code: public void handleMergeRequest(Address sender, MergeId merge_id, Collection<? extends Address> mbrs) {
          merger.handleMergeRequest(sender, merge_id, mbrs);
      }
docs: Get the view and digest and send back both (MergeData) in the form of a MERGE_RSP to the sender.
  If a merge is already in progress, send back a MergeData with the merge_rejected field set to true.
  @param sender The address of the merge leader
  @param merge_id The merge ID
  @param mbrs The set of members from which we expect responses