Bug fix for version 4.2 after I discovered that MySQL version 4 processes the IN operator with a different precidence than version 5 does. Queries that worked fine on my version 5 test server didn't work right at all on our version 4 production server. Version 4.21 simply adds needed parenthesis to the SQL queries so that the results will be the same in any version of MySQL.

Complete contribution attached, only catalog/dynamic_sitemap.php and admin/create_xml_sitemaps have changed.

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