Adds respond_to? handler for subscribers

@vanchi-zendesk @grosser @steved555 - doing this so that [this](https://github.com/rails/rails/blob/3-2-stable/railties/lib/rails/rack/logger.rb#L15) will return true so that we can maybe eventually tag production logs with a short request uuid for better collation.
never mind. saw the code just above this.