update-notifier should not run for non-admins

[Allison Karlitskaya]

when users who are unable to run 'sudo' are logged in the update-notifer runs
and notifies them that updates are available. when they click on it it asks for
their password and even if they enter the correct password, they are unable to
do anything.

update-notifier should check on startup if the user is in the admin group and
exit if not.

[Dennis Kaarsemaker (dennis)]

I suggest that both update-manager and the notificatoin bulb check whether the
user is in the admin group, which is a proposed approach for the menus too.

[Michael Vogt (mvo)]

The problem is that there is currently no way to tell if the user is a sudoer
for that command or not. The "check-admin" group appraoch works most of the time
but fails for system that are upgraded from warty (there wasn't a admin group
back then) or for administrators that added users to suoders by hand.

[Michael Vogt (mvo)]

The gnome-panel/menu has a similar problem with there "X-GNOME-RootRequired=yes"
feature:
https://wiki.ubuntu.com/GnomePanelEnhancementsIdeas

It looks like using the "adm" group will work on all versions of ubuntu. I'll
verify that and use it if it turns out the be a working solution.

[Michael Vogt (mvo)]

Correction:
After some talking on irc it looks like the solution for this problem is:
- check for the existance of the admin group first and do nothing if it does not
exit
- if it exists, check if the user is part of that group

[Sebastien Bacher (seb128)]

that bug is fixed with the dapper package