log-slow-queries replaced with slow_query_log_file

As of MySQL 5.1.29, use --slow_query_log[={0|1}] to enable or disable the slow query log, and optionally --slow_query_log_file=file_name to specify a log file name. The --log-slow-queries option is deprecated.
Reference: http://dev.mysql.com/doc/refman/5.1/en/slow-query-log.html