Do not use deprecated glib function g_atexit().

BUG=http://code.google.com/p/ibus/issues/detail?id=1489

Review URL: https://codereview.appspot.com/6454158

client/x11/main.c

@@ -1214,7 +1214,7 @@ main (int argc, char **argv)
     signal (SIGTERM, _sighandler);
 
     if (_kill_daemon)
-        g_atexit (_atexit_cb);
+        atexit (_atexit_cb);
 
     _xim_init_IMdkit ();
     gtk_main();