code: function() {
      var ret = [];
      this.forEach(function(k){
        if (a_indexOf(ret, k)<0) ret.push(k);
      });
      return ret;
    }
docs: Returns a new enumerable that contains only unique values.  The default
  implementation returns an array regardless of the receiver type.
  
  var arr = ["a", "a", "b", "b"];
  arr.uniq(); => ["a", "b"]
  
  @returns {Ember.Enumerable}