empty string as keyword argument 

If a function is defined with an empty string as default argument like this:

```
def f(a=""):
    pass
```

 this empty string is not shown in the suggestions window.

---
- Bitbucket: https://bitbucket.org/bobf/bpython/issue/153
- Originally Reported By: Anonymous
- Originally Created At: 2010-10-02T00:06:24.878
