Comment 4 for bug 757248

An SFTPServer is instantiated for each authenticated SFTP session, so: A) it doesn't touch until the first SFTP user authenticates, despite it being required for FTP, and B) each new session will create the LoopingCall, and they won't be destroyed until the end.

I'm rolling this back. I'd suggest moving the scheduling into poppy-sftp.tac. Apart from that it looks OK.