For better forward-security support, add functions

SSL_[CTX_]set_not_resumable_session_callback.

Submitted by: Emilia Kasper (Google)

[A part of this change affecting ssl/s3_lib.c was accidentally commited
separately, together with a compilation fix for that file;
see s3_lib.c CVS revision 1.133 (http://cvs.openssl.org/chngview?cn=19855).]