4th Solution to #734

void
MSet::Internal::set_new_weights(double weight, int i) {
    if(i ==0)
        max_attained = weight;
    items[i].wt = weight;
    max_attained = max(max_attained,items[i].wt);
}

void
Mset::set_new_weights_helper(double weight,int i)
{
    internal->set_new_weights(weight,i);
}

template <typename Iterator>
void
MSet::set_new_weights(Iterator first, Iterator last) {
    int i=0;
    for (Iterator it=first;it!=last;++it)
    {
        set_new_weights_helper(*it,i);
        ++i;
    }
}


void
Ranker::rank(Xapian::MSet & mset, const string & model_key, const Xapian::FeatureList & flist)
{
    LOGCALL(API, std::vector<Xapian::docid>, "Ranker::rank", mset | model_key | flist);
    std::vector<FeatureVector> fvv = flist.create_feature_vectors(mset, letor_query, Xapian::Database(db_path));
    load_model_from_metadata(model_key);
    std::vector<FeatureVector> rankedfvv = rank_fvv(fvv);/*Not sorted, The FeatureVectors are in the original order of the  documents*/

    std::vector<double> weights;
    for (size_t i = 0; i < rankedfvv.size(); ++i) {
        weights.push_back(rankedfvv[i].get_score());
    }

   mset.set_new_weights(weights);
}