Pierre-Yves David <pierre-yves.david@fb.com> [Fri, 22 May 2015 10:48:11 -0500] rev 25421
sshpeer: introduce a "doublepipe" class
This class is responsible for ensuring we still process the server output
streamed through the ssh's 'stderr' pipe during the initial wait for other
protocol streams.
It currently only works on posix system because of its use of 'select.select'.