Use www.gnu.org as example hostname in manual (bug 10014)

[Roland McGrath]

> On Thu, 6 Sep 2012, Roland McGrath wrote:
> 
> > That seems fine, or else "example.com", which is the canonical thing used
> > in RFCs and such.
> 
> I suggested www.example.org in that bug before (in February), and 
> www.gnu.org was what you then suggested!

You were wise to listen to me then.  It might be wise to listen to me now,
but probably the former me had better rationale.