Bug #30444: 5.0 mysqldump silently allows wrong backup to be taken against a 4.0 database

The combination of --single-transaction and --master-data requires
START TRANSACTION WITH CONSISTENT SNAPSHOT which is available from
mysqld 4.1 on. When trying this against an older server, print
diagnostic, then, if --force is not given, abort.

No test-case given since it would require a mysqld < 4.1.

client/mysqldump.c

@@ -2428,6 +2428,18 @@ static int start_transaction(MYSQL *mysql_con)
     need the REPEATABLE READ level (not anything lower, for example READ
     COMMITTED would give one new consistent read per dumped table).
   */
+  if ((mysql_get_server_version(mysql_con) < 40100) && opt_master_data)
+  {
+    fprintf(stderr, "-- %s: the combination of --single-transaction and "
+            "--master-data requires a MySQL server version of at least 4.1 "
+            "(current server's version is %s). %s\n",
+            ignore_errors ? "Warning" : "Error",
+            mysql_con->server_version ? mysql_con->server_version : "unknown",
+            ignore_errors ? "Continuing due to --force, backup may not be consistent across all tables!" : "Aborting.");
+    if (!ignore_errors)
+      exit(EX_MYSQLERR);
+  }
+
   return (mysql_query_with_error_report(mysql_con, 0,
                                         "SET SESSION TRANSACTION ISOLATION "
                                         "LEVEL REPEATABLE READ") ||