bug#12583: latest org-mode changes exposes bug in `comment-forward' in newcomment.el

[Le Wang]

Repro with Emacs head:

1. emacs -Q
2. create new org file
3. insert "# blah"
4. C-a
5. M-: (comment-forward 1)

The problem is that `comment-use-syntax' changed from 'undecided to
nil in org.el, which intern exposed a problem in `comment-forward':

It contains:

    (re-search-forward comment-end-skip nil 'move)

But comment-end-skip can validly be nil according to documentation.

-- 
Le