Propagate file permissions in both directions in Unix pscp and psftp.

Propagate file permissions in both directions in Unix pscp and psftp.

I think I have to consider this to be a separate but related change to
the wishlist item 'pscp-filemodes'; that was written before the Unix
port existed, and referred to the ability to configure the permissions
used for files copied from Windows to Unix - which is still not done.

[originally from svn r9260]