add refs to builtin loops

[olleicua]

e.g

(for (a (b))
  (stuff))

should compile to

(function() {
  var _collection_ = b();
  for (_i0_ = 0; _i0_ < _collection_.length; _i0_++) {
    (function(a) { stuff(); }).call(this, _collection_[_i0_]);
  }
}).call(this)

[olleicua]

example assumes #16 is done first