Update the sendResponseMessage with a protected modifier and fix a spelling error.

Planning on using this library for a larger project and may be submitting more patches in the future. Just wanted to get this small fix in and see how it goes.

I updated the sendResponseMessage with the protected modifier so subclasses could override it's functionality. Basically a few of us are running into a situation where we need access to the raw HttpResponse object to get at the response headers and status code. If we can override this method we can subclass AsyncHttpResponseHandler and get at those values.