[gsm] Delay the creation of the GsmXSMPClient until it really exists

We used to create the GsmXSMPClient before the XSMP connection is really
accepted. This can lead to some issues, though. An example is:
https://bugzilla.gnome.org/show_bug.cgi?id=598211#c19. Quoting:

 "What is happening is that a new client (probably metacity in your
 case) is opening an ICE connection in the GSM_MANAGER_PHASE_END_SESSION
 phase, which causes a new GsmXSMPClient to be added to the client
 store. The GSM_MANAGER_PHASE_EXIT phase then begins before the client
 has had a chance to establish a xsmp connection, which means that
 client->priv->conn will not be initialized at the point that xsmp_stop
 is called on the new unregistered client."

The fix is to create the GsmXSMPClient object when there's a real XSMP
connection. This implies moving the timeout that makes sure we don't
have an empty client to the XSMP server.

https://bugzilla.gnome.org/show_bug.cgi?id=598211
delete_property (GsmXSMPClient *client,
                 const char    *name)
{
        int     index;
        SmProp *prop;

        prop = find_property (client, name, &index);
        if (!prop) {
                return;
        }

#if 0
        /* This is wrong anyway; we can't unconditionally run the current
         * discard command; if this client corresponds to a GsmAppResumed,
         * and the current discard command is identical to the app's
         * discard_command, then we don't run the discard command now,
         * because that would delete a saved state we may want to resume
         * again later.
         */
        if (!strcmp (name, SmDiscardCommand)) {
                gsm_client_run_discard (GSM_CLIENT (client));
        }
#endif

        g_ptr_array_remove_index_fast (client->priv->props, index);
        SmFreeProperty (prop);
}

delete_property (GsmXSMPClient *client,
                 const char    *name)
{
        int     index;
        SmProp *prop;

        prop = find_property (client, name, &index);
        if (!prop) {
                return;
        }

#if 0
        /* This is wrong anyway; we can't unconditionally run the current
         * discard command; if this client corresponds to a GsmAppResumed,
         * and the current discard command is identical to the app's
         * discard_command, then we don't run the discard command now,
         * because that would delete a saved state we may want to resume
         * again later.
         */
        if (!strcmp (name, SmDiscardCommand)) {
                gsm_client_run_discard (GSM_CLIENT (client));
        }
#endif

        g_ptr_array_remove_index_fast (client->priv->props, index);
        SmFreeProperty (prop);
}
