zope.site.hooks.setSite is always called too late to be usable and it became
a nightmare to make getSite working early enough.

This fixes portal creation on Zope 2.12, which was broken since r38613.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@38691 20353a03-c40f-0410-a6d1-a30d3c3de9de