itertuples() fails after selecting a column twice
The following code gives incorrect result (using pandas 0.11):

``` python
import pandas
df = pandas.DataFrame(data={"a": [1, 2, 3], "b": [4, 5, 6]})
print df[["a", "a"]].values # works
print list(df[["a", "a"]].itertuples()) # FAILS!
```

The last lines prints [(0, 'a', 'a'), (1, 'a', 'a')] instead of [(0, 1, 1), (1, 2, 2), (2, 3, 3)].
