COAttributedStringWrapper: listen for the begin batch and end batch, and call -beginEditing / -endEditing, so that the text view doesn't try to relayout while we are reloading a new state. This is not required for correctness but improves performance for undo/redo.

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10051 7b3f36aa-e6db-49c1-8b4c-66eac1997e64