Show Panics Nicely

Currently if you get a panic in a koan, it looks like this:
![Screen Shot 2013-01-04 at 17 23 24](https://f.cloud.github.com/assets/14548/43712/84d1126a-5693-11e2-948c-96affc413e74.png)

However, this isn't so great for new developers who are likely to be following the koans, so I created a nicer error message (it's the same colour as an assert(false) message, red, just my terminal shows it pink):
![Screen Shot 2013-01-04 at 17 27 02](https://f.cloud.github.com/assets/14548/43722/097ef248-5694-11e2-80e1-c3834ec31ac8.png)

This makes it easier for new developers to use.

I also converted __delete_me__() into a function as it felt nicer, but that commit could be discarded easily.

And yes, the way we find which function it was that panicked is very hacky - we iterate through the callers until we find the first file in the current directory. This is because sometimes the panic() is at different levels of the call-stack.