BUG: iloc getitem with DataFrame with MultiIndex

```
import pandas as pd
import numpy as np

tup = zip(*[['a','a','b','b'],['x','y','x','y']])
index = pd.MultiIndex.from_tuples(tup)
df = pd.DataFrame(np.random.randn(4, 4), index=index)
df.iloc[[0, 1]]
```

This will raise:

```
ValueError: Buffer dtype mismatch, expected 'Python object' but got 'long'
```

I am using 0.12 version.
