bug#10063: 24.0.91; Making font-lock-mode-hook buffer-local while locally let-bound!

[Katsumi Yamaoka]

Stefan Monnier wrote:
>> Why it is defvar'd here is that it no longer exists in Emacs but
>> still exists in XEmacs.  XEmacs people use it to run some support
>> modes `fast-lock', `lazy-lock', etc. as Emacs people use
>> `font-lock-support-mode'.

> A note about it (not near the defvar but near the place where you force
> this var to nil) would be welcome.

Ok.  Done.