sftp server support!
finally check in sftp_handle (file handle abstraction), sftp_si (server
interface), and sftp_server (server implementation) -- all of which make
a roughly 90% implementation of server-side sftp.
don't forget demo_windows.py
update MANIFEST.in to include demo_windows.py and not include the demo
keys (they're in tests/ now). clean up the README to explain the demo
scripts better now, since there are so many of them. then fix up the
demo scripts to look in tests/ for the keys.
demo_windows.py doesn't need to call get_pty() (in fact, i think that's
blowing openssh's mind) and was executing the wrong command.