BUG: setitem with list elements in the indexer broken

```
In [4]: df = DataFrame(np.arange(9).reshape((3, 3)),
                  index=["A", "B", "C"], columns=["A", "B", "C"])

In [5]: df.iloc[[0,1],[1,2]] += 100

In [6]: df.iloc[[0,1],[1,2]]
Out[6]: 
     B    C
A  101  102
B  104  105

In [7]: df
Out[7]: 
   A    B    C
A  0  101  102
B  3  104  105
C  6    7    8
```