WebSite_getDocumentPhysicalPath() was changed and currently always return an object. Use an alternate method to guess if we are at root or not.
Define globals even if no document found.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@8768 20353a03-c40f-0410-a6d1-a30d3c3de9de