* dbusbind.c: Serial number integer overflow fixes.

* dbusbind.c: Serial number integer overflow fixes.

(CHECK_DBUS_SERIAL_GET_SERIAL): New macro.
(xd_invalid_serial): New static function.
(Fdbus_call_method_asynchronously, xd_read_message_1): Use a float
to hold a serial number that is too large for a fixnum.
(Fdbus_method_return_internal, Fdbus_method_error_internal):
Check for serial numbers out of range.  Decode any serial number
that was so large that it became a float.