dist/multilabel/PassiveAggressiveHash.js
function(classes) {
		classes = hash.normalized(classes);
		for (var aClass in classes) {
			if (!(aClass in this.weights)) {
				this.weights[aClass]={};
				this.weights_sum[aClass]={};
			}
		}
	}
function(classes) {
		classes = hash.normalized(classes);
		for (var aClass in classes) {
			if (!(aClass in this.weights)) {
				this.weights[aClass]={};
				this.weights_sum[aClass]={};
			}
		}
	}
Tell the classifier that the given classes will be used for the following
samples, so that it will know to add negative samples to classes that do
not appear.

@param classes an object whose KEYS are classes, or an array whose VALUES are classes.