openssl: Fix build with openssl < ~ 0.9.8f

The symbol SSL3_MT_NEWSESSION_TICKET appears to have been introduced at
around openssl 0.9.8f, and the use of it in lib/vtls/openssl.c breaks
builds with older openssls (certainly with 0.9.8b, which is the latest
older version I have to try with).

lib/vtls/openssl.c

@@ -1427,8 +1427,10 @@ static const char *ssl_msg_type(int ssl_ver, int msg)
         return "Client hello";
       case SSL3_MT_SERVER_HELLO:
         return "Server hello";
+#ifdef SSL3_MT_NEWSESSION_TICKET
       case SSL3_MT_NEWSESSION_TICKET:
         return "Newsession Ticket";
+#endif
       case SSL3_MT_CERTIFICATE:
         return "Certificate";
       case SSL3_MT_SERVER_KEY_EXCHANGE: