attrib: Add quotes to fix the usage message indentation.

[Francois Gouget]

I did not mean to send this patch because it still has the old commit 
description. Please use my other attrib patch instead.


-- 
Francois Gouget <fgouget at free.fr>              http://fgouget.free.fr/
                 Dieu dit: "M-x Lumière". Et la lumière fut.