Support System.register modules in CSP build

Hey @guybedford, trying the latest and greatest again.

This could just be me being confused, but I'd like to use the `System.register` format. However it just fails with a `Include Traceur for module syntax support` error. I don't really understand the error because the module has already been transpiled to ES5 syntax.

![screen shot 2014-05-09 at 5 16 37 pm](https://cloud.githubusercontent.com/assets/137/2933452/3bc5aeba-d7bf-11e3-8653-152b42c1105f.png)