assigning list to series with boolean indexing
Whenever a boolean array is used to assign some list or array to another series, it returns "ValueError: Length of replacements must equal series length". This was working fine in pandas 10.0, but broke with 10.1

``` python
import pandas as pd
import numpy as np
x = pd.Series(np.arange(10))
sel = x < 5
len(x[sel])
x[sel] = range(5) # doesn't work anymore
x[0:5] = range(5) # works
```
