updated for version 7.3.290

Problem:    When a BufWriteCmd autocommand resets 'modified' this doesn't
            change older buffer states to be marked as 'modified' like
            ":write" does.  (Yukihiro Nakadaira)
Solution:   When the BufWriteCmd resets 'modified' then adjust the undo
            information like ":write" does.