* lisp/emacs-lisp/smie.el (smie-auto-fill): Rework to be more robust.

* lisp/emacs-lisp/smie.el (smie-auto-fill): Rework to be more robust.
(smie-setup): Use add-function to set it.

* lisp/progmodes/octave.el (octave-smie-rules): Return nil rather than
0 after a semi-colon; it works better for smie-auto-fill.
(octave--indent-new-comment-line): New function.
(octave-indent-new-comment-line): Use it (indirectly).
(octave-mode): Don't disable smie-auto-fill.  Use add-function to
modify comment-line-break-function.