ts by contrast receive variable length cells with differing rules on
their arrival. As such making a best effort attempt at a send-and-receive
method in which we do the following...

  * Discard any existing unread data from the socket.
  * Send our request.
  * Await up to a second for a reply.

It's quite possible this is a stupid approach. If so, patches welcome.

:param stem.client.cell.Cell cell: cell to be sent

:returns: **generator** with the cells received in reply
r