[BUGFIX beta] IE8 fixes for beta

6 failures left to go. Everything major seems to be locked down, though this also requires that https://github.com/tildeio/htmlbars/pull/91 be merged and the dependency in Ember be updated.

* [ ] Update the dependency to HTMLBars
* [ ] Triage the final 6 failure with @rwjblue, fix anything remaining

Review of this and the HTMLBars PR very welcome.
can we do the fast inline version of this?

```js
function MetalRenderer() {
  this._super$constructor();
}

MetalRenderer.prototype._super$constructor = Renderer
```