bug#13816: 24.3.50; turn-on-font-lock doesn't turn it on

[Katsumi Yamaoka]

Recently turn-on-font-lock set to some hook turns font-lock
on but turns it off immediately regardless of the value of
global-font-lock-mode.  Here's a recipe:

emacs -Q
Eval: (add-hook 'emacs-lisp-mode-hook 'turn-on-font-lock)
and visit some .el file.

In Emacs 24.2, it works no matter what global-font-lock-mode is.
Thanks.