bug#20951: 25.0.50; emacs -nw hangs during startup

[Ken Brown]

emacs -nw -Q, run from an xterm terminal, appears to hang during startup
before it finishes displaying the *scratch* buffer.  I have to kill it
from another terminal.  A bisection shows that the problem started with
the following commit:

commit cc8f96e6e19ad3f56631f432e088590a8cf8535d
Author: Stefan Monnier <monnier@iro.umontreal.ca>
Date:   Tue Jun 30 23:20:29 2015 -0400

    * lisp/term/xterm.el (xterm--query): Avoid generating garbage

    (xterm-query-timeout): New var.
    (xterm--query): Use it.  Fallback on async method if we timeout before
    getting the first byte of the reply (bug#12354).

In GNU Emacs 25.0.50.11 (x86_64-unknown-cygwin, GTK+ Version 3.14.13)
 of 2015-07-01 on moufang
Repository revision: 3d759f4f6f2a20abbc05225a55d35c5daf093ff6
Windowing system distributor `The Cygwin/X Project', version 11.0.11701000
Configured using:
 `configure 'CFLAGS=-g3 -O0''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS NOTIFY ACL
GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
%