COSQLiteStore: store backing store <-> persistent root UUID in a separate table, that is append-only. Fixs -testAccessItemGraphAfterPersistentRootDeletion

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10181 7b3f36aa-e6db-49c1-8b4c-66eac1997e64