update-manager failure when clicking on 'Settings'

[Jean-Philippe Orsini]

To reproduce:
 - launch 'update-manager'
 - a window popup 'The software on this computer is up to date'
 - click on 'Settings...' => no reponse

The output is:
Traceback (most recent call last):
  File "/usr/bin/software-properties-gtk", line 37, in <module>
    from softwareproperties.gtk.SoftwarePropertiesGtk import SoftwarePropertiesGtk
  File "/usr/lib/python3/dist-packages/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 34, in <module>
    from aptdaemon import client
  File "/usr/lib/python3/dist-packages/aptdaemon/client.py", line 43, in <module>
    import gobject as GObject
ImportError: No module named gobject

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: update-manager 1:0.167
ProcVersionSignature: Ubuntu 3.5.0-5.5-generic 3.5.0-rc7
Uname: Linux 3.5.0-5-generic i686
ApportVersion: 2.4-0ubuntu3
Architecture: i386
CurrentDmesg.txt:
 [ 18.666758] [drm] Initialized drm 1.1.0 20060810
 [ 18.681276] [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
 [ 18.681280] [drm] No driver support for vblank timestamp query.
 [ 18.681284] [drm] Initialized vboxvideo 1.0.0 20090303 for 0000:00:02.0 on minor 0
 [ 20.469610] init: plymouth-stop pre-start process (1237) terminated with status 1
Date: Fri Jul 20 19:03:38 2012
GsettingsChanges:
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'launch-time' b'1342803794'
 b'com.ubuntu.update-manager' b'show-details' b'true'
 b'com.ubuntu.update-manager' b'window-height' b'634'
 b'com.ubuntu.update-manager' b'window-width' b'1167'
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release i386 (20120423)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)