COAttributedStringWrapper: Fix -edited:range:changeInLength: call in response to object graph changes. Fixes undo in some simple cases

git-svn-id: svn://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@9978 7b3f36aa-e6db-49c1-8b4c-66eac1997e64