COObject: Move isZombie to Debugging section. Tweak the description a bit to emphasize that it is for debugging only. I removed the code example suggesting calling -loadedObjectForUUID: to re-fetch the object because I think that should be done in response to COObjectGraphContext notifications only (they are a bit lacking in documentation unfortunately)

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10320 7b3f36aa-e6db-49c1-8b4c-66eac1997e64