fix a bug : before this fix, when you create a new System Preference, a tales was showing you that the priority was "Site" but in fact, the property was not defined (unless the user save using the graphical interface). Now this default property is set using a init script. Tales is no longer required.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@38754 20353a03-c40f-0410-a6d1-a30d3c3de9de