bug#632: 23.0.60; Turning off visual-line-mode ignores previous value of truncate-lines

[Lawrence Mitchell]

If a buffer with `truncate-lines' set to t is put in
visual-line-mode and subsequently visual-line-mode is turned off,
the value of truncate-lines is lost (it is set to the default value).

Steps to reproduce:

1) emacs -Q
2) evaluate

(progn
  (switch-to-buffer (generate-new-buffer "bug"))
  (setq truncate-partial-width-windows nil)
  (setq-default truncate-lines nil)
  (setq truncate-lines t)
  (insert (make-string (+ (window-width) 10) ?a))
  (goto-char (point-min))
  (visual-line-mode -1))

Expected result:
truncate-lines is t in the buffer "bug"

Actual result:
truncate-lines is nil (the default value).

In GNU Emacs 23.0.60.1 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2008-07-24 on lamacq.ph.ed.ac.uk
Windowing system distributor `The X.Org Foundation', version 11.0.60802000
configured using `configure  '-C' 
'--prefix=/scratch/s0198183/applications/emacs-trunk/' 'CFLAGS=-ggdb3 -O0''

Cheers,
Lawrence

-- 
Lawrence Mitchell <wence@gmx.li>