BUG: CategoricalIndex can't be a boolen mask

```python
In [1]: import pandas as pd

In [2]: idx = pd.CategoricalIndex([True, False, True])

In [3]: pd.Series(range(3))[idx]
Out[3]:
True    NaN
False   NaN
True    NaN
dtype: float64
```

Expected:


```python
In [4]: pd.Series(range(3))[idx.astype(object)]
Out[4]:
0    0
2    2
dtype: int64
```

Fix coming shortly.