§ 257. Covenants bind representatives of grantor and mortgagor and inure to the benefit of whom. All covenants contained in any grant or mortgage of real estate bind the heirs, executors, administrators, successors and assigns, of the grantor or mortgagor, and inure to the benefit of the heirs, executors, administrators, successors and assigns of the grantee or mortgagee in the same manner and to the same extent, and with like effect as if such heirs, executors, administrators, successors and assigns were so named in such covenants, unless otherwise in said grant or mortgage expressly provided.