Fix Error_InvalidModuleDeclaration.module.js on Windows

This error reported looks like:

File not found 'c:\src\traceur\test\feature\Modules\resources\no_such_file.js'

We were not correctly normalizing this error.

Fixes #1322
We write all the expected errors with forward slashes.

We typically even skip the path and filename since the test is only using one file anyway. The typical expected error is defined as 

```js
// Error: :8:17: Unexpected token ;
```

But sometimes we a use a leading partial path. This is important mostly for module tests since they work with multiple files and we want to ensure that the error is reported in the correct file

```js
// Error: feature/Modules/Error_ImportDefault.js:4:8: 'default' is not exported by ...
```
https://github.com/arv/traceur-compiler/blob/master/test/feature/Modules/Error_ImportDefault.js#L2

Then we have errors that are reported by the import/export validator. These include paths in the actual message. These are always relative to `/test/` and always start with `feature/`. These errors have normalized paths already.

```js
// Error: :7:9: 'w' is not exported by 'feature/Modules/resources/x'
```

And then finally we have the file not found error which is generated by Node.js using a OS dependent and checkout dependent path. That is the only case we can get different results on different OS and different checkouts.