Added ThresholdProducingMetric interface for metrics that compute thresholds for class probabilities. Also adapted IterativeClassifierOptimizer to make use of this functionality.

git-svn-id: https://svn.cms.waikato.ac.nz/svn/weka@10945 e0a1b77d-ad91-4216-81b1-defd5f83fa92
LogitBoost now implements BatchPredictor and can use multi-threading when batch prediction is used. IterativeClassifierOptimizer now has a step size parameter.

git-svn-id: https://svn.cms.waikato.ac.nz/svn/weka@10946 e0a1b77d-ad91-4216-81b1-defd5f83fa92