Remove support for pre-authentication compression. Doing compression
early in the protocol probably seemed reasonable in the 1990s, but
today it's clearly a bad idea in terms of both cryptography (cf.
multiple compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.
cleanup_exit(int i)
{
	if (the_authctxt) {
		do_cleanup(the_authctxt);
		if (use_privsep && privsep_is_preauth &&
		    pmonitor != NULL && pmonitor->m_pid > 1) {
			debug("Killing privsep child %d", pmonitor->m_pid);
			if (kill(pmonitor->m_pid, SIGKILL) != 0 &&
			    errno != ESRCH)
				error("%s: kill(%d): %s", __func__,
				    pmonitor->m_pid, strerror(errno));
		}
	}
	_exit(i);
}

cleanup_exit(int i)
{
	if (the_authctxt) {
		do_cleanup(the_authctxt);
		if (use_privsep && privsep_is_preauth &&
		    pmonitor != NULL && pmonitor->m_pid > 1) {
			debug("Killing privsep child %d", pmonitor->m_pid);
			if (kill(pmonitor->m_pid, SIGKILL) != 0 &&
			    errno != ESRCH)
				error("%s: kill(%d): %s", __func__,
				    pmonitor->m_pid, strerror(errno));
		}
	}
	_exit(i);
}
