Fixed missing -objectEnumerator implementation in COMutableDictionary (required by GNUstep)

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10108 7b3f36aa-e6db-49c1-8b4c-66eac1997e64
Removed -[COGroup contentArray] to just use the inherited implementation (-allObjects cannot be sent to an array on GNUstep)

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10109 7b3f36aa-e6db-49c1-8b4c-66eac1997e64