Lists as elements of DataFrame
Changing a DataFrame element which is a list, works only when the length of the list is not larger then two.

``` python
df = DataFrame({"a":[[1,2,3], [4,5,6]], "b":[[1,2],[3,4]]})
df.iloc[0,1] = [1,20] #works
df.iloc[0,0] = [1,2,30] #throws exception
ValueError: Must have equal len keys and valuewhen setting with an iterable
```

The behavior is the same for numpy-arrays and tuples.
Is the use of lists as elements of a DataFrame not allowed in pandas?
## INSTALLED VERSIONS

pandas: 0.13.1
Cython: 0.15.1
numpy: 1.8.1
scipy: 0.13.3
