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.)

git-svn-id: svn://svn.tartarus.org/sgt/putty@1264 cda61777-01e9-0310-a592-d414129be87e