Move some cleanup stuff after X terminates

[Alkis Georgopoulos]

Most of the things in ltsp-trunk/client/localapps/ldm-rc.d/X99-zlocalapps-cleanup should happen after X is terminated, for 2 reasons:
 * When the X9* scripts run, X is still running, along with many local user processes, so for example ~/.gvfs is still in use, and `fusermount -uqz ${LDM_HOME}` fails. That results in many problems when fat client or localapps users log in for a second time.
 * In case X crashes, these script won't get to run at all, so it'd be safer to do the cleanup from a process that isn't killed when X dies (so not from within ldm).

That's what X99-ltsp-logout-action is trying to do too: it postpones the reboot/shutdown action for after X termination, to be processed by XS00-halt-reboot. It would make more sense if all those evens run on the "stop" event of ldm-script, but unfortunately currently the "stop" event happens while X is still running, so it's not different from the X9* scripts.
I think it'd be better if the "stop" event was launched after X terminates. Maybe some screen-session.d/XK00-* script could launch it.
Btw X99-zzz-logout-action should be deleted, its functionality has been moved to X99-ltsp-logout-action.

[Alkis Georgopoulos (alkisg)]

Fix committed mostly in http://bazaar.launchpad.net/~ltsp-upstream/ltsp/ltsp-trunk/revision/2429 and in http://bazaar.launchpad.net/~ltsp-upstream/ltsp/ldm-trunk/revision/1458.

Importance set to medium as there was a possibility for data loss:
 * User logs in, using a fat client or localapps,
 * Then logs out,
 * fusermount -uqz forcibly unmounts "$LDM_HOME",
 * User processes that are still running write back their data *locally* in the tmpfs "$LDM_HOME",
 * And in the next login of the same user, sshfs refuses to mount "$LDM_HOME" because "nonempty" wasn't set, so the user can't see his documents/settings, and any new documents he creates are lost on logout.

[Alkis Georgopoulos (alkisg)]

It's still not fixed, as the ssh socket is closed by LDM too early, before the `fusermount -u` call.

For a real solution, I propose that LDM runs outside X.
Due to a lack of .C maintainers, I also propose that LDM is rewritten in shell. There were some objections for that, though. And hopefully we'll switch to LightDM in a couple of years and LDM will be deprecated.

So until the problem is solved correctly, I'll implement a hack in shell that forcibly kills all user processes on logout and does the cleanup before X dies.

[Alkis Georgopoulos (alkisg)]

The plan to move LDM outside of X was abandoned due to the move to LightDM.
A script that kills all local user processes on logout was committed instead, in
http://bazaar.launchpad.net/~ltsp-upstream/ltsp/ltsp-trunk/revision/2462.
It's highly suggested that distros affected by this bug, backport that commit,
and of course users can manually apply it if their distros won't backport it.

[Alkis Georgopoulos (alkisg)]

Fix released in LTSP 5.4.6 (http://bazaar.launchpad.net/~ltsp-upstream/ltsp/ltsp-trunk/revision/2502).