Better reporting for mismatched item UUIDs accross identical object graph contexts 
(to be less a pain to debug since it tends to arise easily).


git-svn-id: svn://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@9931 7b3f36aa-e6db-49c1-8b4c-66eac1997e64