Cpython units

This is the start of a feature branch for getting the cpython unittests to work.

Unless we are willing to modify the way imports are done in each of the cpython unit tests, our first big hurdle is to fix the missing feature of import that lets us import modules from a package:

Specifically:

```python
from test import test_support
...
test_support.run_unittests()
```

I've made a naive start to this in the __import__ function in import.js, but its not quite right.

Would love ideas from others on how to do this the right way.