System.register update

This includes the System.register update corresponding to the new format implemented into Traceur here - https://github.com/google/traceur-compiler/pull/1161.

All tests are passing!
I do the same in the microloader, but I also keep track of the values thru a proxy object, and that's the one I hand over when calling `System.import()`, I wonder how are you creating the proxy for `moduleObj`?