Turned on Serialization and Diff tests on GNUstep.

TestDiffManager is presently disabled since it depends on Test/Extras/Model.

All enabled tests pass.

Note: This requires GNUstep Base from trunk to get fast enumeration working 
for class clusters, and proper NSValueTransformer subclass registration.


git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10029 7b3f36aa-e6db-49c1-8b4c-66eac1997e64