Set discriminating_bscore::_full_bscore to true

I compared learning using prerec given some table with 251 features
for discriminating_bscore::_full_bscore set to true and false about
measured no difference. So I set discriminating_bscore::_full_bscore
to true as it's makes diversity work better (2x better according to my
measurements).
Merge pull request #135 from ngeiswei/set_default_prerec_bscore

Set discriminating_bscore::_full_bscore to true