Poor RS485Settings exception messages

[astrelsky]

These exception messages should state that they are not supported on the platform instead of saying the value is unsupported. I had to dig up the source to figure out why any float value I entered for delay_before_tx was invalid.

pyserial/serial/serialwin32.py

Lines 183 to 204 in 3a6ae5a

	# checks for unsupported settings
	# XXX verify if platform really does not have a setting for those
	if not self._rs485_mode.rts_level_for_tx:
	raise ValueError(
	'Unsupported value for RS485Settings.rts_level_for_tx: {!r}'.format(
	self._rs485_mode.rts_level_for_tx,))
	if self._rs485_mode.rts_level_for_rx:
	raise ValueError(
	'Unsupported value for RS485Settings.rts_level_for_rx: {!r}'.format(
	self._rs485_mode.rts_level_for_rx,))
	if self._rs485_mode.delay_before_tx is not None:
	raise ValueError(
	'Unsupported value for RS485Settings.delay_before_tx: {!r}'.format(
	self._rs485_mode.delay_before_tx,))
	if self._rs485_mode.delay_before_rx is not None:
	raise ValueError(
	'Unsupported value for RS485Settings.delay_before_rx: {!r}'.format(
	self._rs485_mode.delay_before_rx,))
	if self._rs485_mode.loopback:
	raise ValueError(
	'Unsupported value for RS485Settings.loopback: {!r}'.format(
	self._rs485_mode.loopback,))

[zsquareplusc]

OK, why not. Added accepted value to the error message.