fixing a bug that made the management tabs disappear for some
property sheets involving ZClasses.

such as PropertySheets, are traversable but are not Items.

Thanks to Gisle Aas.

(index_html).

  * Now products can specify that their help topics are viewed as part of an existing product using the registerHelpTitle method. This allows us to visually join OFSP, MailHost and other standard Zope products.

  * API docs are now represented as belonging to a sub 'API Documentation' node.

without them :(

parse it :(