This corrects the reference count handling in SSL_get_session.

Previously, the returned SSL_SESSION didn't have its reference count
incremented so the SSL_SESSION could be freed at any time causing
seg-faults if the pointer was subsequently used. Code that uses
SSL_get_session must now make a corresponding SSL_SESSION_free() call when
it is done to avoid memory leaks (or blocked up session caches).

Submitted By: Geoff Thorpe <geoff@eu.c2.net>