import/export broken because of IIFE

I was examining our options for #50 and came across some annoying behavior. Because the compiler wraps everything in an IIFE, I can't seem to run generated ES6 module code through Traceur. For example, I ended up with code along the lines of:

``` es6
"use strict";
(function() {
import A from "A";
function B() { }
export default B;
})();
```

but that won't fly because Traceur expects the `import` to be outside of the IIFE.

For now, I've added an extra task to my Gruntfile to strip out the IIFE. However, we should either have a way to make the IIFE optional, or, preferably, hoist the imports out of it and return the exports from it.

(Or am I doing something horribly wrong? I'm basically compiling my code to ES6, then creating a System.js build from it, and finally loading it in Chrome. With the IIFE patch, that works well.)