Serial port that do not implement the full feature set can't be opened

When an opened device does not implement all the features of a "true" serial port, some settings may not work. Thus, the following:

    if (!d->setBaudRate()
        || !d->setDataBits(d->dataBits)
        || !d->setParity(d->parity)
        || !d->setStopBits(d->stopBits)
        || !d->setFlowControl(d->flowControl)) {
        // || !d->setDataTerminalReady(d->dataTerminalReady) // THIS FAILS
        // || !d->setRequestToSend(d->requestToSend)) {      // THIS FAILS AS WELL
        close();
        return false;
    }

will end up closing a working serial port. For example, a PTY serial port opened by socat will not necessarily have DTR and RTS working. Thus, I suggest that in case those fail, we leave the serial port opening, and emit an error to the user so he can decide to deal or not with the problem.