Comment 2 for bug 43731

here's a patch that changes SingleListener to SocketListener and keeps listening for new connections until explicitly asked to stop (via TestCase.tearDown).

this lets the sftp unit tests continue to pass, but that means nothing since they don't try to use multiple connections yet. :)

if i comment out the connection cache using this patch, one of the tests locks up pretty quickly. i haven't had a chance to look at that yet, but i will continue later.