ERR: invalid error reporting when comparing vs. None
The "in" function does not work as expected in regard to a data frame. Let's say we have the following data frame :

`df = pd.DataFrame(np.random.randn(6,4), columns=list('ABCD'))`

We can test this data frame :

```
df is None
False
```

However we cannot test its presence in a list : 

```
df in [None]
TypeError: Could not compare [None] with block values
```

We would expect to get just False in this case.

(Pandas version 0.17.1)
