Show browser engine version

When running tests, buster prints the browser version, but it would be helpful to see the browser engine version too. When I attach both the released Safari browser and the WebKit nightly build buster prints:

```
Safari 5.1.2 OS X:     .
Safari 5.1.2 OS X (2): .
```

It would be nice to see something like:

```
Safari 5.1.2 (WebKit 534.52.7) OS X: .
Safari 5.1.2 (WebKit 536.2+) OS X:   .
```
