bug#17497: 24.4.50; TTY menu glitches

[Eli Zaretskii]

> From: Andreas Schwab <schwab@suse.de>
> Date: Thu, 05 Jun 2014 10:29:14 +0200
> Cc: 17497@debbugs.gnu.org
> 
> Thomas Dickey <dickey@his.com> writes:
> 
> > start with
> >     static bool get_input_pending (int);
> >
> > The code's waiting for a while to ensure that it gets all of the bytes in
> > a cursor-key/function-key/mouse-event sequence.
> 
> No, it doesn't.  It just reads whatever is pending, without paying
> attention to key boundaries.

In addition, the function which reads keys isn't called during menu
updates, because we call update_frame_1 with its argument force_p
non-zero, so update_frame_1 doesn't even pay attention whether there's
input available.