In a conveyance of real estate the words "quitclaim covenant" shall have the full force, meaning and effect of the following words: "The grantor covenants with the grantee, his heirs and assigns that he will warrant and forever defend the premises to the said grantee, his heirs and assigns forever, against the lawful claims and demands of all persons claiming by, through or under him."   [PL 1967, c. 377 (NEW).]