bug#25547: 25.1.91; emacsclient -c creates frames on the wrong display

[Alex Hutcheson]

When an emacsclient running in a terminal is connected to an Emacs
instance running in a graphical environment, running `emacsclient -c'
from a comint buffer (such as M-x shell) creates a frame in the
graphical environment, where it may be inaccessible to the user who
ran the command.

To reproduce:
1. Run `emacs --daemon' on a system with a graphical display.
2. Login to the system using a terminal with no graphical display. You
   could do this by switching to another virtual terminal (Ctrl-Alt-F1
   works on Ubuntu), or SSH in from another machine.
3. Run `emacsclient -c' or `emacsclient -t' in the terminal to connect
   to the running Emacs instance.
4. Inside Emacs, run M-x shell.
5. In the M-x shell buffer, run `emacsclient -c'.

Ideal behavior: emacsclient creates a frame on the current terminal.
Actual behavior: emacsclient creates a graphical frame in the
  environment in which it was launched, which is inaccessible from the
  terminal.

Possible questions:

Q : Why would you want to run emacsclient from within M-x shell? Why
    not just do whatever you want to do in the frame you already have
    open?
A : Normally the user isn't launching emacsclient directly. Instead,
    a script might be launching emacsclient as part of a larger
    workflow.

Q : Why not just launch emacsclient without the '-c' option?
A : Without the -c flag, emacsclient works well to edit a file or
    series of files, but it doesn't support more complicated tasks.
    For example, a script might want to launch an ediff session, and
    wait until the ediff session exits. The easiest way to do this is
    to use `emacsclient -c' and wait for the connection to be closed.


In GNU Emacs 25.1.91.1 (x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars),  
modified by Debian
Windowing system distributor 'The X.Org Foundation', version 11.0.11501000
System Description:     Ubuntu 14.04 LTS

Configured using:
 'configure --build x86_64-linux-gnu --build x86_64-linux-gnu
 --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
  
--enable-locallisppath=/etc/google-emacs:/etc/emacs:/usr/local/share/emacs/25.1.91+gg1+2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1.91+gg1+2/site-lisp:/usr/share/emacs/site-lisp
 --with-crt-dir=/usr/lib/x86_64-linux-gnu --disable-build-details
 --disable-silent-rules --with-modules GOOGLE_VERSION=25.1.91+gg1+2
 --with-x=yes --with-x-toolkit=lucid --with-toolkit-scroll-bars
 --without-gconf --without-gsettings build_alias=x86_64-linux-gnu
 'CFLAGS=-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat
 -Werror=format-security -Wall' 'LDFLAGS=-Wl,-Bsymbolic-functions
 -Wl,-z,relro -Wl,-fuse-ld=gold,--export-dynamic-symbol=__google_auxv'
 'CPPFLAGS=-D_FORTIFY_SOURCE=2 -DGOOGLE_EMACS_DEFINE_AUXV''

Configured features:
XAW3D XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS NOTIFY
LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS LUCID X11 MODULES

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Message

Minor modes in effect:
  mml-mode: t
  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
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  auto-fill-function: message-do-auto-fill
  transient-mark-mode: t
  abbrev-mode: t

Recent messages:
Sending...
Mark set
Fix continuation lines? (y or n) y [59 times]
Mark set
Sending via mail...
if: Mail headers not found
Mark set
Sending...
Mark set [2 times]
Sending via mail...
if: Mail headers not found

Load-path shadows:
None found.

Features:
(pp shadow sort mail-extr emacsbug message format-spec rfc822 mml
mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
google-sendgmr sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils novice cl-extra help-fns help-mode easymenu misearch
multi-isearch dired-aux cl-loaddefs pcase cl-lib dired time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel x-win term/common-win x-dnd tool-bar dnd fontset
image regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cl-generic cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote dbusbind inotify dynamic-setting
font-render-setting x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 111409 15495)
 (symbols 48 20120 0)
 (miscs 40 211 363)
 (strings 32 15788 3029)
 (string-bytes 1 498060)
 (vectors 16 12877)
 (vector-slots 8 445607 5773)
 (floats 8 175 297)
 (intervals 56 4381 159)
 (buffers 976 29)
 (heap 1024 34656 1309))