A covenant or agreement by the grantor or grantors, in any deed or instrument in writing for conveying or releasing land that he, they, or it “will warrant generally the property hereby conveyed,” shall have the same effect as if the grantor or grantors had covenanted that he or they, his or their heirs and personal representatives or successors, will forever warrant and defend the said property, and every part thereof, unto the grantee, his heirs, personal representatives and assigns, against the lawful claims and demands of all persons whomsoever.