gwt-d3: Workaround Double/Boolean unboxed in GWT 2.8

BooleanDatumFunction.java

// package protected because its internal
interface BooleanDatumFunction {
	public boolean apply(Element context, Value d, int index);
}

DatumFunction.java

public interface DatumFunction<T> {
	public T apply(Element context, Value d, int index);
}

Selection.java

// make it a Java method
public final Selection classed(String classNames, DatumFunction<Boolean> addFunction) {
  return classed(classNames, new BooleanDatumFunction() {
    public boolean apply(Element context, Value d, int index) {
      Boolean ret = addFunction.apply(context, d, index);
      return ret == null ? false : ret.booleanValue();
    }
  });
};

private native final Selection classedImpl(String classNames, BooleanDatumFunction addFunction)/*-{
  return this.classed(
  		classNames,
  		function(d, i) {
  			// always returns primitive boolean now
  			// JSNI Shortcut notation
  			return addFunction.@BooleanDatumFunction::apply(*)(this,{datum:d},i);
  		});
}-*/;