Improved DTLS rehandshake test to catch a timeout issue in handshake().
reinitialize the handshake timers when gnutls_handshake() is called.
doc update
Verify in example that the sent nonce matches the received nonce.

Reported by Benny Baumann.
fix small leak
When sending a nonce in OCSP check if it is available on the reply.
When verifying a response and a signer isn't provided assume that the signer is the issuer.
doc update