Optional reconnect functionality

Enable the server to request the client to reconnect.

This can be done with the now extended minetest.request_shutdown([reason], [reconnect]) setting.

src/client.h

@@ -489,6 +489,8 @@ public:
 	bool accessDenied()
 	{ return m_access_denied; }
 
+	bool reconnectRequested() { return m_access_denied_reconnect; }
+
 	std::string accessDeniedReason()
 	{ return m_access_denied_reason; }
 
@@ -636,6 +638,7 @@ private:
 
 
 	bool m_access_denied;
+	bool m_access_denied_reconnect;
 	std::string m_access_denied_reason;
 	std::queue<ClientEvent> m_client_event_queue;
 	bool m_itemdef_received;