Improve Search request with selected atttributes

When searching for some entries, selecting specific attributes, we could improve the performance by avoiding a lookup() call.

The CollectiveAttributeInterceptor addCollectiveAttributes() method is looking for a "collectiveAttributeSubentries" attribute which is not present in the returned entry. The reason is that the search engine remove all attributes which have not been specifically requested before returning the result, which is then processed by the interceptors.

Adding another SearchResultFilter (for instance, in the NormalizingInterceptor) which will remove the attributes not requested by the user and keeping all the user and operational attributes in the serach engine will allow a great boost in performance by avoid a useless lookup (estimated to 30%).