bug#22641: 24.5; Double import on completion in python mode

[vsuharnikov]

Steps for reproduce:
* start emacs: emacs -Q
* create an empty python buffer: C-x b foo.py RET
* turn on python mode: M-x python-mode RET
* start interpreter: C-c C-z (python-shell-switch-to-shell) and answer the 
prompts (I pressed RET n)
* switch back to python buffer: C-x o (other-window)
* type "from os import " (there is a space after "import")
* press C-M-i (completion-at-point)

Observed behaviour: "import " is inserted in the buffer. The buffer now 
contains "from os import import ".
Expected behaviour: completion-at-point offers names from the os module 
as completion candidates.



In GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 2.24.29)
 of 2016-01-26 on fort_dey
Windowing system distributor `The X.Org Foundation', version 11.0.11800000
System Description:     Gentoo Base System release 2.2

Configured using:
 `configure --prefix=/usr --build=x86_64-pc-linux-gnu
 --host=x86_64-pc-linux-gnu --mandir=/usr/share/man
 --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc
 --localstatedir=/var/lib --disable-dependency-tracking
 --disable-silent-rules --libdir=/usr/lib64 --program-suffix=-emacs-24
 --infodir=/usr/share/info/emacs-24 --localstatedir=/var
 --enable-locallisppath=/etc/emacs:/usr/share/emacs/site-lisp
 --with-gameuser=:gamestat --without-compress-install
 --with-file-notification=inotify --enable-acl --with-dbus
 --without-gnutls --with-gpm --without-hesiod --without-kerberos
 --without-kerberos5 --without-xml2 --without-selinux --without-wide-int
 --with-zlib --with-sound=alsa --with-x --without-ns --without-gconf
 --without-gsettings --without-toolkit-scroll-bars --with-gif
 --with-jpeg --with-png --with-rsvg --with-tiff --with-xpm
 --without-imagemagick --with-xft --without-libotf --without-m17n-flt
 --with-x-toolkit=gtk2 GENTOO_PACKAGE=app-editors/emacs-24.5-r1
 'CFLAGS=-march=native -O2 -pipe -nopie' CPPFLAGS= 'LDFLAGS=-Wl,-O1
 -Wl,--as-needed''

Important settings:
  value of $LC_ALL: 
  value of $LANG: ru_RU.utf8
  locale-coding-system: utf-8-unix

Major mode: Python

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:
C-x C-g is undefined
Quit [3 times]
Make dedicated process? (y or n) n
Sent python-shell-completion-setup-code
Sent python-ffap-setup-code
Sent python-eldoc-setup-code
No match
Making completion list...
Quit
Making completion list...

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 compile cl-extra help-mode python
easymenu json comint ring cl-loaddefs cl-lib ansi-color time-date
cyril-util 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 inotify dynamic-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 86333 7207)
 (symbols 48 18744 0)
 (miscs 40 59 199)
 (strings 32 12885 4754)
 (string-bytes 1 391566)
 (vectors 16 10730)
 (vector-slots 8 400620 7751)
 (floats 8 69 423)
 (intervals 56 343 0)
 (buffers 960 14)
 (heap 1024 13190 827))