Add a new parameter to the getSiteMapTree : exclude_default_document.
This makes it possible to hide the default documents from a website
menu when 
they are already displayed at the top of the menu for instance.
This change is backward compatible : the default behaviour is the old one.



git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@31710 20353a03-c40f-0410-a6d1-a30d3c3de9de