Tor uses these values to implement a low-rent clone of RFC 5705 (which,
in our defense, we came up with before RFC 5705 existed).  But now that
ssl_st is opaque, we need another way to get at them.

Includes documentation, with suitable warnings about not actually
using these functions.
Signed-off-by: NNick Mathewson <nickm@torproject.org>
Signed-off-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NTim Hudson <tjh@openssl.org>