COSerialization: Add automatic handling of NSDate using Java semantics. Rationale is, dates are probably more common that other types we already support (point, size, rect, range)

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@9998 7b3f36aa-e6db-49c1-8b4c-66eac1997e64