Comment 2 for bug 22105

Just to flesh my idea out:

When a package requires a reboot for it work properly, it creates an empty file
(e.g. "/var/lib/update-notifier/require-reboot")

update-notifier spots this and then shows a 'stock' notification text, e.g:

--
<b>Reboot required</b>

Parts of your base system have been upgraded. You should
reboot your machine soon to ensure the upgrades are effective.
--

Once the message has been shown to the user (or a reboot happens),
update-notifier would remove the file.

Although (obviously) update-notifier can't enforce this policy, there could be
an ubuntu policy so that all the ubuntu packages that need reboots just have to
touch the file. I just didn't like being told that dbus needed a reboot, and
immediately hal needed one :-)