Simplify CORevisionCache by having object lifetime controlled by a strong pointer in COEditingContext. This avoids the refcounting implementation which was accomplishing the same thing afaik. BTW, thanks for finding the gigantic COSQLiteStore leak :-)

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10118 7b3f36aa-e6db-49c1-8b4c-66eac1997e64