psftp and pscp should disable all forwarding (ports, X, agent).

psftp and pscp should disable all forwarding (ports, X, agent).
Partly because that's a good idea _anyway_, and partly because it
seems to be causing trouble. (Specifically, their pathetic attempt
to emulate plink's proper select handling seems to get confused when
the back end tries to open a local listening socket.)

[originally from svn r1264]