Fix a PAM_USER mismatch in session open/close. We update PAM_USER

Fix a PAM_USER mismatch in session open/close.  We update PAM_USER
to the target user immediately before setting resource limits, which
is after the monitor process has forked (so it has the old value).
Also, if the user did not authenticate, there is no pamh in the
monitor so we need to init pam here too.  This means we end up
calling pam_start() twice, which should be fixed, but at least the
session is always properly closed now.

--HG--
branch : 1.8