Attempt to pretty print response data with text/javascript content-type header as json

```
Some APIs incorrectly use text/javascript as the content-type for JSON content 
(application/json is the only valid JSON mime type), but we should be flexible 
and attempt to pretty print such content as JSON (and fail silently if the 
content is not in fact JSON).
```

Original issue reported on code.google.com by `stephen....@gmail.com` on 11 Mar 2013 at 10:14
