Fix GuessEntityName

Both SessionFactoryImpl.GuessEntityName and NHibernateUtil.GuessEntityName implementations are broken because, when they are called with a proxy (all objects of lazy classes are proxies) they do not return the proper type name (that of the mapped class, not the proxy). This prevents usage of ISession.Replicate, ISession.SaveOrUpdate, etc, because NHibernate cannot find a persister for the proxy class (MappingException: no persister for xxxxProxy). Instead, both implementations might instead use something like NHibernateProxyHelper.GuessClass(entity).FullName.