the default page item doesn't necessarily live in the folder itself

plone doesn't remove the `default_page` property when renaming or deleting an item.  `getDefaultPage` only returns `None` when no item of that name can be acquired, though.  hence, the item needs to be acquired to match that logic...
add change log entry for `getDefaultPage` fix
Merge pull request #16 from witsch/deleted-default-page

the default page item doesn't necessarily live in the folder itself