Incorrect ValueError message
I am trying to replace values in a Series with recalculated values, but I get the following error:

```
ValueError: Length of replacements must equal series length
```

However, looking at the lengths of the original values and the replacements, there does not seem to be a problem:

```
In [151]: len(children.wfa[not_null])

Out[151]: 2945

In [152]: len(np.array(wfa))

Out[152]: 2945

In [153]: children.wfa[not_null] = np.array(wfa)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-153-798afd63872b> in <module>()
----> 1 children.wfa[not_null] = np.array(wfa)

/Library/Python/2.7/site-packages/pandas-0.11.0.dev_7996a8c_20130313-py2.7-macosx-10.8-intel.egg/pandas/core/series.pyc in __setitem__(self, key, value)
    811         if _is_bool_indexer(key):
    812             key = _check_bool_indexer(self.index, key)
--> 813             self.where(~key,value,inplace=True)
    814         else:
    815             self._set_with(key, value)

/Library/Python/2.7/site-packages/pandas-0.11.0.dev_7996a8c_20130313-py2.7-macosx-10.8-intel.egg/pandas/core/series.pyc in where(self, cond, other, inplace)
    731             other = other.reindex(ser.index)
    732         if len(other) != len(ser):
--> 733             raise ValueError('Length of replacements must equal series length')
    734 
    735         result, changed = com._maybe_upcast_putmask(ser,~cond,other)

ValueError: Length of replacements must equal series length
```

Unfortunately the data I am using is private medical data, so I cannot post the dataset for anyone to look at. However, if there is anything I can do to assist in debugging this, I am willing to iterate through it to get to the bottom of the problem.

Running pandas-0.11.0.dev_7996a8c_2013031 on Python 2.7.2 on OS X 10.8.3.
