initialized after the call to pthread_create() instead of before. It just
happened to work with threads enabled because ctxt is shared, but of
course it doesn't work when we use a child process instead of threads.
Reimplement the necessary bits from auth_pam.c and auth2_pam.c so that
they share the PAM context used by the keyboard-interactive thread. If
a child process is used instead, they will (necessarily) use a separate
context.
Constify do_pam_account() and do_pam_session().
Sponsored by: DARPA, NAI Labs
