* bus/dispatch.c (bus_dispatch): make this return proper
	DBusHandlerResult to avoid DBUS_ERROR_UNKNOWN_METHOD

	* dbus/dbus-errors.c (dbus_set_error): use
	_dbus_string_append_printf_valist

	* dbus/dbus-string.c (_dbus_string_append_printf_valist)
	(_dbus_string_append_printf): new

	* dbus/dbus-errors.h (DBUS_ERROR_UNKNOWN_MESSAGE): change to
	UNKNOWN_METHOD

	* dbus/dbus-connection.c (dbus_connection_dispatch): handle
	DBUS_HANDLER_RESULT_NEED_MEMORY; send default error reply if a
	message is unhandled.