.erb files can proxy others

Would help my ruby dev a lot. Have some .erb files that run through a compile/replace:

```javascript
/**
 * ./app/assets/javascripts/global-vars.js.erb
 * Loaded into the head of a document and responsible for currying global confs
 */

window.SA = window.SA = {
  default_logo_url: '<%= asset_path("default_community_property.jpg") %>'
};
```

Tested in local project -- happy to come back and add tests if you think this should be merged.