Added a new late-bound references API to ETEntityDescription and 
ETPropertyDescription, while still supporting the old model (can be removed later).

This new API eliminate memory management issues and complexity involving unecessary 
-iString checks.

Note: All previous methods such as -setOpposite: used inside +newEntityDescription 
are now superceded. For example, -setOppositeName: exists to replace -setOpposite:.
All tests pass in EtoileFoundation, CoreObject and EtoileUI.


git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/EtoileFoundation@10319 7b3f36aa-e6db-49c1-8b4c-66eac1997e64