Fixed broken incoming relationships when both relationship sides are in the same 
persistent object graph context

Note: The problem doesn't exist accross persistent roots, or in the same transient 
object graph context, this is why it doesn't appear in Relationship tests. 
We need to come up with some solution to exercise all Relationship tests in 
the following situations at least:

- references in the same transient object context (we just cover this case currently)
- references in the same persistent object context
- references accross transient object contexts
- references accross persistent object graph contexts

More in TODO.


git-svn-id: svn://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@9925 7b3f36aa-e6db-49c1-8b4c-66eac1997e64