Allow non-root apps to suggest user log back in

Currently, we have a mechanism for root to notify any logged-in users that they should reboot the machine.

But there are some situations where the user merely needs to re-login. For example, we currently have a dpkg trigger when a package that is upgrading from gconf to gsettings that triggers the 'reboot machine' message. When all such a thing really needs is a new X session.

In a similar way, non-root apps might want to trigger such a notice. In particular, my pet project Deja Dup is a backup program that, when restoring, would like to notify the user to log out and back in to get any settings that have been updated by the restore.

So the request is for:
A) A "log back in" message system to complement the current "reboot" message
B) A way for non-root apps to trigger the "log back in" message

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: update-notifier 0.112ubuntu1
ProcVersionSignature: Ubuntu 3.0-1.2-generic 3.0.0-rc3
Uname: Linux 3.0-1-generic i686
Architecture: i386
Date: Thu Jun 23 13:34:42 2011
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110422)
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, user)
 LANG=en_US.utf8
 LC_MESSAGES=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: update-notifier
UpgradeStatus: No upgrade log present (probably fresh install)