Add response body validation

### What is the problem / feature ?

It'd be good if response validation actually looked at the response body.  (it currently doesn't)

### How did it get fixed / implemented ?

Implemented a `data` property on the `flex.http.Response` object to represent the response data, and added validation against it.

### How can someone test / see it ?

Validate a response?

*Here is a cute animal picture for your troubles...*

![sun-bear1](https://cloud.githubusercontent.com/assets/824194/4962918/7941fe28-66ef-11e4-8259-16ba4f72cc8a.jpg)