sslutils: Check if OpenSSL supports SSLv2.

Recent versions/builds seem to disable that feature.

plugins/sslutils.c

@@ -55,7 +55,12 @@ int np_net_ssl_init_with_hostname_and_version (int sd, char *host_name, int vers
 			method = TLSv1_client_method();
 			break;
 		case 2: /* SSLv2 protocol */
+#ifdef OPENSSL_NO_SSL2
+			printf (("%s\n", _("CRITICAL - SSL Protocol Version 2 is not supported by your build of OpenSSL.")));
+			return STATE_CRITICAL;
+#else
 			method = SSLv2_client_method();
+#endif
 			break;
 		case 3: /* SSLv3 protocol */
 			method = SSLv3_client_method();