It was only actually used in X11 and port forwarding, to find internal
state structures given only the Socket that ssh.c held. So now that
that lookup has been reworked to be the sensible way round,
private_ptr is no longer used for anything and can be removed.
[originally from svn r10075]
This isn't yet used, but I plan to use it in situations where you have
to report errors by returning a valid Socket on which the client wlil
call sk_socket_error, but in fact you notice the error _before_
instantiating your usual kind of Socket. The resulting Socket is
usable for nothing except reading out the error string and closing it.
[originally from svn r10065]
Simon Tatham