bug#4738: 23.1.50; Inconsistent mouse-1 on url in rcirc

[Chong Yidong]

> >> If I remember correctly, it used to be the case that only mouse-2
> >> visited hyperlinks in emacs buffers.  Is it standard for mouse-1 to do
> >> this now?  Should I just change the binding, or duplicate it?
> >
> > Use the "follow-link" functionality.  See the "Defining Clickable Text"
> > node in the Emacs Lisp manual; you can look at the way other Emacs modes
> > do it for examples.
>
> I tested the following patch and it seems to work correctly.

Thanks, I went ahead and checked it in.