code: public MergingIterator<ZooPC> loadAllInstances(Class<?> cls, 
  			boolean subClasses, boolean loadFromCache) {
  		checkActiveRead();
  		MergingIterator<ZooPC> iter = 
  				new MergingIterator<ZooPC>(this, config.getFailOnClosedQueries());
          ZooClassDef def = cache.getSchema(cls, primary);
  		loadAllInstances(def.getVersionProxy(), subClasses, iter, loadFromCache);
  		if (loadFromCache) {
  			//also add 'new' instances
  			iter.add(cache.iterator(def, subClasses, ObjectState.PERSISTENT_NEW));
  		}
  		return iter;
  	}
docs: INTERNAL !!!!
  @param cls Class
  @param subClasses whether to load subclasses
  @param loadFromCache whether to load from cache or only from DB
  @return An extent over a class