Redact request body in HTTPStatusError message

When `request[:body]` is a String, I think this should be removed. Something like:

```rb
request[:body] = REDACTED if request.has_key?(:body) && !request[:body].respond_to?(:path)
```

Not only to hide possibly sensitive information, but when `request[:body]` is something like `@file.read(5+MB)`, it makes for one whale of an error message.