Small cleanup, double entry in CHANGES.

     This fixes a DoS attack. (CVE-2013-0166)

     [Steve Henson]

  *) Return an error when checking OCSP signatures when key is NULL.

     This fixes a DoS attack. (CVE-2013-0166)

     [Steve Henson]

  *) Call OCSP Stapling callback after ciphersuite has been chosen, so

     the right response is stapled. Also change SSL_get_certificate()

     so it returns the certificate actually sent.