Moved runtime inclusion to after compilation, due to generator hoisting

The loader works great, though not with generators. The reason is the following issue : [https://github.com/google/traceur-compiler/issues/1141](https://github.com/google/traceur-compiler/issues/1141). 

So I moved the inclusion of the runtime after the compilation of the file content. That way it is ensured that the require statement is at the very top of the file, not causing the $traceurRuntime to not exist when using generators. Using generators causes usage of the runtime to be hoisted at the very top of the file, even above the require of the runtime. Crash and burn :-)

Thanks for putting this together!