vim-patch:7.4.1988

Problem:    When updating viminfo with file marks there is no time order.
Solution:   Remember the time when a buffer was last used, store marks for
            the most recently used buffers.
ab9c89b68d

As this is a viminfo fix, most of this is irrelevant - the patch has
just been brought across for the creation and updating of buffer's
`b_last_used` properties.

src/nvim/buffer.c

@@ -1618,6 +1618,7 @@ void enter_buffer(buf_T *buf)
   if (!curbuf->b_help && curwin->w_p_spell && *curwin->w_s->b_p_spl != NUL) {
     (void)did_set_spelllang(curwin);
   }
+  curbuf->b_last_used = time(NULL);
 
   redraw_later(NOT_VALID);
 }