[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.
This is a test helper, not even a lukewarm path. I'd like to lean toward the least surprising thing in this case. If this is a pattern that would be good to adapt across the board for internals I can make a big patch for it over the codebase