Made all Store and StorageDataModel tests pass on GNUstep.

Note: This requires GNUstep Base from trunk to get JSON serialization working 
correctly.


git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10016 7b3f36aa-e6db-49c1-8b4c-66eac1997e64