Int64Index.max() raises a TypeError exception
On my computer, the following code raises a `TypeError: len() of unsized object` on line 171 of `core\index.py`:

```
pd.Int64Index(range(10)).max()
```

Similarly for `min()`, but `mean()` works.

Pandas version: 0.10.0
System: Windows 8 64 bits
Python 2.7.3 64 bits
