Fix script newline escaping with expanded assets

If config.assets.debug = true is set, the jquery.ui.all.js is expanded into several smaller required scripts. This means the javascript_include_tag returns newlines that need to be escaped to generate valid code.

Without this fix using force: true in development generates a parsing error. Chrome reports:
```
Uncaught SyntaxError: Unexpected token ILLEGAL
```

By urlencoding the newline character we can fix this.