OpenSSh privilege separation model - http://www.citi.umich.edu/u/provos/ssh/privsep.html
Posix_spawn is implemented in POSIX adapter as an alternative to fork() that is heavily used in Privilege separation.
Additional state info is added to sshd to accommodate distinguishing the various modes (privileged monitor, unprivileged child, authenticated child).
Required service state (like config and host keys) is transmitted over pipes from monitor to child processes.
Changes to installation scripts and tests to accomodate new architectural changes
client now connect to ssh-agent at Identification level, preventing rogue processes hosting "ssh-agent" pipes from impersonating and elevating to client context.
Since ssh-agent now cannot do ImpersonateNamedpipeClient, retrieve the client impersonation token explicitly and rely on ImpersonateLoggedonUser instead.
