Loosing series names, when concatenating into DataFrame
In the version 9.1, when we are concatenating pandas.Series, we would expect the columns name of the created DataFrame to be the ones of the Series which were concatenated together. Nevertheless the series' names are lost, and the columns are simply 0, 1, 2 ...

Error shown below:

``` python
pd.__version__
Out[14]: '0.9.1rc1'

s1 = pd.TimeSeries(randn(5), index=pd.date_range('01-Jan-2013', periods=5, freq='D'), name='A')

s2 = pd.TimeSeries(randn(5), index=pd.date_range('01-Jan-2013', periods=5, freq='D'), name='B')

series = [s1, s2]

pd.concat(series, axis=1)



_32.columns = map(lambda s: s.name, series)

_32




```
