Try to fix bug#5314. This is probably not the final word, tho.

Try to fix bug#5314.  This is probably not the final word, tho.
* buffer.c (Fset_buffer_modified_p): Try and be careful not to modify
recent-auto-save-p as a side-effect.
* buffer.h (BUF_AUTOSAVE_MODIFF): New macro.
* buffer.c (Fkill_buffer, reset_buffer):
* editfns.c (Fsubst_char_in_region):
* fileio.c (Finsert_file_contents, Fdo_auto_save)
(Fset_buffer_auto_saved, Frecent_auto_save_p): Use it.