Exit after the user's session has finished.  This works around slim's broken
PAM session handling (see
http://developer.berlios.de/bugs/?func=detailbug&bug_id=19102&group_id=2663).

Patch by Eelco Dolstra, from Nixpkgs.

--- slim-1.3.6/app.cpp	2013-10-15 11:02:55.629263422 +0200
+++ slim-1.3.6/app.cpp	2013-10-15 13:00:10.141210784 +0200
@@ -816,7 +822,7 @@
 	StopServer();
 	RemoveLock();
 	while (waitpid(-1, NULL, WNOHANG) > 0); /* Collects all dead childrens */
-	Run();
+	exit(OK_EXIT);
 }
 
 void App::KillAllClients(Bool top) {
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<tr><td><span title='2019-08-15 07:43:09 -0400'>2019-08-15</span></td><td><a href='/guix/commit/gnu/machine.scm?id=9c70c460a05b2bc60f3f3602f0a2dba0f79ce86c'>machine: Implement 'roll-back-machine'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/machine.scm (roll-back-machine, &amp;deploy-error, deploy-error?)
(deploy-error-should-roll-back)
(deploy-error-captured-args): New variable.
* gnu/machine/ssh.scm (roll-back-managed-host): New variable.
* guix/scripts/deploy.scm (guix-deploy): Roll-back systems when a
deployment fails.
</span></span></td><td>Jakob L. Kreuze</td></tr>
<tr><td><span title='2019-08-06 15:48:51 -0400'>2019-08-06</span></td><td><a href='/guix/commit/gnu/machine.scm?id=d97ce20400b5d2967bfbc0e9fbfb99bbb2daed4f'>machine: Rename 'system' field.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/machine.scm (machine-system): Delete variable.
(machine-operating-system): New variable.
All callers changed.
* doc/guix.texi (Invoking guix deploy): Use the
'machine-operating-system' accessor rather than 'machine-system'.
</span></span></td><td>Jakob L. Kreuze</td></tr>
<tr><td><span title='2019-07-06 02:10:04 -0400'>2019-07-06</span></td><td><a href='/guix/commit/gnu/machine.scm?id=fa9edf09e992db7510c7471486dffc93e1e707e5'>gnu: Add machine type for deployment specifications.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/machine.scm: New file.
* gnu/machine/ssh.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
</span></span></td><td>Jakob L. Kreuze</td></tr>