COSQLiteStore: turn on single-database mode for now. Last time I tested it, it was slower, but now it's around 15% faster for both the test and benchmark targets (probably from removing the overhead of creating all of the backing stores the tests use).

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10126 7b3f36aa-e6db-49c1-8b4c-66eac1997e64