Update Metamorph helpers, fixes invalid markup bug in IE9

- See bug in this jsbin: http://jsbin.com/ilikaj/1/ (in IE9)
- I pulled the branch for PR #2166 and cherry-picked the commit
- Only an update of craigteegarden/ember.js/commit/914f41121d
- Updated the jsbin: http://jsbin.com/ilikaj/3/ resolves IE9 bug

[Fixes #2018]