Behavior of Series.values when dtype is "category" is surprising
Say I make a category-type Series:

``` python
s = pd.Series(["a", "b", "c"], dtype="category")
```

I want to pass this to a function that expects a numpy array, so I use the `values` property. According to the documentation:

``` python
s.values?
```

```
Type:        property
String form: <property object at 0x106d84050>
Docstring:
Return Series as ndarray

Returns
-------
arr : numpy.ndarray
```

However:

``` python
s.values
```

```
[a, b, c]
Categories (3, object): [a < b < c]
```
