ETUUID: avoid any message sends in -isEqual: in the common case. this version is around 4x faster than the previous

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/EtoileFoundation@10518 7b3f36aa-e6db-49c1-8b4c-66eac1997e64