In a conveyance of real estate the words "warranty covenants" shall have the full force, meaning and effect of the following words: "The grantor covenants with the said grantee, his heirs and assigns that he is lawfully seized in fee of the premises, that they are free of all encumbrances, that he had good right to sell and convey the same to the said grantee to hold as aforesaid, and that he and his heirs shall and will warrant and defend the same to the said grantee, his heirs and assigns forever, against the lawful claims and demands of all persons."   [PL 1967, c. 377 (NEW).]