SerialPort::clear

[thepperson]

The SerialPort::Clear function seems to do really wonky stuff to the receive buffer in async code. I see a lot of messages repeated twice and partial messages when I use the async function read_to_end
I am calling clear on a SerialStream object.

[iynehz]

I also got some issue with SerialPort::clear but in a different senario,

After I get the SerialStream object via open_native_async(), I do a clear(All), then I write async to serial bus the first message and there is ideally response coming from serial. But in this case it can't get anything to the read buffer.

In contrast, if I do clear(Output) or if I don't do clear() at all, it works good and I can read the response.