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='2017-01-25 14:05:37 +0100'>2017-01-25</span></td><td><a href='/guix/commit/gnu/services/spice.scm?id=e57bd0bed86caac304e5f37c5653e6b13858c7c5'>services: Fix 'mkdir-p' in activation scripts.</a><span class='msg-avail'>...</span></td><td>Clément Lassieur</td></tr>
<tr><td><span title='2016-09-10 13:10:06 +0200'>2016-09-10</span></td><td><a href='/guix/commit/gnu/services/spice.scm?id=9e41130b14ad32c4e1fa756f95d806703056cb60'>system: Use 'file-append' to denote file names.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-08-05 21:48:43 +0200'>2016-08-05</span></td><td><a href='/guix/commit/gnu/services/spice.scm?id=00f469056893ae80fecefee44e09d6904b613de4'>services: Add spice vdagent service.</a><span class='msg-avail'>...</span></td><td>David Craven</td></tr>