Bugfix: exception is now displayed in last failed step when there are multiple failed steps

Related to issue #191 and pull request #352.
Before:
![_001](https://cloud.githubusercontent.com/assets/2046080/4100784/07664176-30b5-11e4-982d-73f50f2ab889.png)


After:
![_002](https://cloud.githubusercontent.com/assets/2046080/4100785/0cfc1408-30b5-11e4-9917-3a5adf9a827c.png)

jfyi, you can create a copy of array before reversing

```js
var hasFailed = step.steps.slice(0).reverse().some(findFailedStep);
```