concat with axis=1, join='outer' not working correctly
http://stackoverflow.com/questions/11761884/pandas-concatouter-not-doing-union

```

It looks pandas.concat is doing 'left outer' join instead of just union the indexes. Seems a bug to me but maybe I'm missing something obvious.

    import pandas
    import pandas.util.testing as put
    ts1 = put.makeTimeSeries()
    ts2 = put.makeTimeSeries()[::2]
    ts3 = put.makeTimeSeries()[::3]
    ts4 = put.makeTimeSeries()[::4]

    ## to join with union
    ## these two are of different length!
    pandas.concat([ts1,ts2], join='outer', axis = 1) 
    pandas.concat([ts2,ts1], join='outer', axis = 1)
Any idea how can I get the full union (as they do claim by using join='outer' on the pandas document)

Thanks.
```
