Tab completion in IPython 6 on Categorical shows warning
With pandas 0.20.1, IPython 6.0.0 (stack from conda-forge) I have:

```python
In [31]: obj = pd.Categorical(['foo', 'bar', 'baz'])

In [32]: obj.<TAB>
/home/wesm/miniconda/envs/book-env/lib/python3.6/site-packages/jedi/evaluate/compiled/__init__d
  getattr(obj, name)
```

I'm not sure the origin or meaning in the output, but it's a bad smell that may confuse users