code: func descendantBlock(prevHash *chainhash.Hash, curBlock *btcutil.Block) error {
  	curHash := &curBlock.MsgBlock().Header.PrevBlock
  	if !prevHash.IsEqual(curHash) {
  		rpcsLog.Errorf("Stopping rescan for reorged block %v "+
  			"(replaced by block %v)", prevHash, curHash)
  		return &ErrRescanReorg
  	}
  	return nil
  }
docs: // descendantBlock returns the appropriate JSON-RPC error if a current block
  // fetched during a reorganize is not a direct child of the parent block hash.