message: do nothing in push_block if adding block does not change fork_db head
diff: @@ -505,7 +505,7 @@ struct controller_impl {
  fork_db.set_validity( new_head, false ); // Removes new_head from fork_db index, so no need to mark it as not in the current chain.
  throw;
  }
  - } else {
  + } else if( new_head->id != head->id ) {
  auto branches = fork_db.fetch_branch_from( new_head->id, head->id );
  for( auto itr = branches.second.begin(); itr != branches.second.end(); ++itr ) {
  