Implement the Opaque PRF Input TLS extension

(draft-rescorla-tls-opaque-prf-input-00.txt), and do some cleanups and
bugfixes on the way.  In particular, this fixes the buffer bounds
checks in ssl_add_clienthello_tlsext() and in ssl_add_serverhello_tlsext().

Note that the opaque PRF Input TLS extension is not compiled by default;
see CHANGES.

apps/s_cb.c

@@ -638,6 +638,11 @@ void MS_CALLBACK tlsext_cb(SSL *s, int client_server, int type,
 		extname = "server ticket";
 		break;
 
+#ifdef TLSEXT_TYPE_opaque_prf_input
+		case TLSEXT_TYPE_opaque_prf_input:
+		extname = "opaque PRF input";
+		break;
+#endif
 
 		default:
 		extname = "unknown";

apps/s_client.c

@@ -859,6 +859,11 @@ bad:
 		}
 #endif	/* OPENSSL_NO_KRB5  */
 /*	SSL_set_cipher_list(con,"RC4-MD5"); */
+#if 0
+#ifdef TLSEXT_TYPE_opaque_prf_input
+	SSL_set_tlsext_opaque_prf_input(con, "Test client", 1);
+#endif
+#endif
 
 re_start:
 
@@ -1073,11 +1078,13 @@ re_start:
 			if (in_init)
 				{
 				in_init=0;
+#if 0 /* This test doesn't really work as intended (needs to be fixed) */
 #ifndef OPENSSL_NO_TLSEXT
 				if (servername != NULL && !SSL_session_reused(con))
 					{
 					BIO_printf(bio_c_out,"Server did %sacknowledge servername extension.\n",tlsextcbp.ack?"":"not ");
 					}
+#endif
 #endif
 				if (sess_out)
 					{

apps/s_server.c

@@ -1575,6 +1575,11 @@ static int sv_body(char *hostname, int s, unsigned char *context)
 						 strlen((char *)context));
 	}
 	SSL_clear(con);
+#if 0
+#ifdef TLSEXT_TYPE_opaque_prf_input
+	SSL_set_tlsext_opaque_prf_input(con, "Test server", 1);
+#endif
+#endif
 
 	if (SSL_version(con) == DTLS1_VERSION)
 		{