Diff/COArrayDiff.m: Fix some compiler warnings

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10406 7b3f36aa-e6db-49c1-8b4c-66eac1997e64
Fix some COCommand vs COCommandGroup compiler warnings

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10407 7b3f36aa-e6db-49c1-8b4c-66eac1997e64