bug#7137: two dashes appear after long y-or-n-p's

[Eli Zaretskii]

> From: jidanni@jidanni.org
> Date: Thu, 30 Sep 2010 07:31:40 +0800
> Cc: 
> 
> (y-or-n-p "this short question is quite normal ")
> (y-or-n-p "however, with this longer question, be it containing
> newlines or not, if it is beyond a certain width, like this one here
> is on my terminal, a very funny \"--\" appears after the question.
> Test it with C-x C-e OK? ")
> It doesn't happen with yes-or-no-p.
> emacs-version "24.0.50.1"

Probably the result of revno 101415:

  2010-09-12  Stefan Monnier  <monnier@iro.umontreal.ca>

          * subr.el (y-or-n-p): New function, moved from src/fns.c; use 
read-key.

It causes read_key_sequence to be called, which calls echo_prompt,
which calls echo_now, which calls echo_dash, which displays the
dashes.