bug#21456: 24.5; Emacs does not respect fcitx as GTK input method

[Zachary Acreman <zakk@acreman.net>]

Emacs compiled with GTK does not respect fcitx as the system-wide GTK
input method.

When I use a keyboard configuration with right-alt mapped to Compose, I
get "<Multi-key> is undefined" messages in Emacs instead of the expected
behavior.

When I use a keyboard configuration with dead keys for accented
characters, I get messages like "<dead-acute> is undefined" instead of
the expected behavior.

Chinese Pinyin input methods are ignored.

XMODIFIERS=@im=fcitx
GTK_IM_MODULE=fcitx

fcitx input works correctly in every other application on this system
that I have tested.

I am using a freshly downloaded and compiled 24.5 source distribution,
because I saw the same problems with the Ubuntu-provided 24.4
package. For the purposes of this bug report, I am running the binary
with the -Q flag.

In GNU Emacs 24.5.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.13)
  of 2015-09-10 on guru
Windowing system distributor `The X.Org Foundation', version 11.0.11701000
System Description:    Ubuntu 15.04

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

Major mode: Lisp Interaction

Minor modes in effect:
   tooltip-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
   transient-mark-mode: t

Recent messages:
Menu-Bar mode disabled
Menu-bar mode disabled.  Use M-x menu-bar-mode to make the menu bar appear.
Menu-Bar mode enabled
Quit
Making completion list...
Quit
<Multi_key> is undefined [5 times]
@im=fcitx
Making completion list... [2 times]
Quit

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
help-fns mail-prsvr mail-utils help-mode easymenu cus-start cus-load
time-date tooltip electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel x-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment lisp-mode prog-mode register page menu-bar
rfn-eshadow timer select scroll-bar mouse jit-lock font-lock syntax
facemenu font-core frame cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese hebrew greek romanian slovak
czech european ethiopic indian cyrillic chinese case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer 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 make-network-process dbusbind gfilenotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty emacs)

Memory information:
((conses 16 78990 7449)
  (symbols 48 18422 0)
  (miscs 40 41 99)
  (strings 32 10686 3295)
  (string-bytes 1 276107)
  (vectors 16 8990)
  (vector-slots 8 384103 17853)
  (floats 8 65 423)
  (intervals 56 227 16)
  (buffers 960 13)
  (heap 1024 44666 967))