PSCP now uses the modern SFTP protocol if it can, and falls back to

PSCP now uses the modern SFTP protocol if it can, and falls back to
scp1 if it can't. Currently not very tested - I checked it in as
soon as it completed a successful recursive copy in both directions.
Also, one known bug: you can't specify a remote wildcard, because by
the nature of SFTP we'll need to implement the wildcard engine on
the client side. I do intend to do this (and use the same wildcard
engine in PSFTP as well) but I haven't got round to it yet.

git-svn-id: svn://svn.tartarus.org/sgt/putty@1208 cda61777-01e9-0310-a592-d414129be87e