Cyclic references leak memory

```
var foo;

while (true) {
   var x = {};
   var y = {x: x, a: []};
   x.y = y;

   foo = x;

   for (var i = 0; i < 1000000; i++) y.a[i] = i;
}

console.log(foo);
```

Open top and watch it gobble memory.