fix(super): `super()` now means call the proto of the current function.

See [traceur](https://github.com/google/traceur-
compiler/commit/6732e5eddf203ae02bcfb8faea837590bf32c061) for more details

The new semantic works with the Traceur version we use so that this could be merged right now.

(Sorry, for the mess deleting my branch, I had to do this to trigger Travis)