Support IE 9 and lower better

Although it is already supported, the problem is that the back-end
expects 2 extra metaframes, if a stack trace was generated by us.

The first approach in `generateStacktrace()` provides these frames,
but if it fails, we fall back to the second approach, which lacks
them. It means that on the back-end side the parser chops off two
important frames.

![screenshot 2014-08-20 21 22 50](https://cloud.githubusercontent.com/assets/1079123/3991809/07092a94-28eb-11e4-873f-524b5ff0efd1.png)

I'm really surprised that this works reliably. Have you tested it in ie 6 7 and 8 separately?