[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.
It is weird. I can get rid of this with some refactoring upstream in HTMLBars, maybe.

The first argument is the parent node of the morph. The second argument is the contextualElement for any children created inside the morph on that parent.

We pass the contextual separately to avoid `appendMorph` falling back to document.body if the `target` is a document fragment. Basically we are ensuring that we fail hard and fast if there is not an appropriate contextualElement (a real tag) passed explicitly.