/**
   *  Concatenates the observable sequences obtained by running the specified result selector for each element in source.
   * There is an alias for this method called 'forIn' for browsers <IE9
   * @param {Array} sources An array of values to turn into an observable sequence.
   * @param {Function} resultSelector A function to apply to each item in the sources array to turn it into an observable sequence.
   * @returns {Observable} An observable sequence from the concatenated observable sequences.
   */
  Observable['for'] = Observable.forIn = function (sources, resultSelector, thisArg) {
    return enumerableOf(sources, resultSelector, thisArg).concat();
  };