Some various fixes + log in *scorer::ignore_idxs
Compress ctable when feature selection within moses is use

This can greatly speed up evaluation (5x faster on a dataset with 60K
row and 1500 features, while selecting around 10 features).

Add to that it also updates the target score to stop deme search when
the best actual best candidate is found.

WARNING:

1) it relies on some horrible hack of CTable::filtered_preverse_idxs
as a result it only works for binary features

2) it also only works for precision_bscore, in order to take advantage
of that optimization you must implement ignore_idxs in your scorer.