Multiple series for FRED data
I haven't looked under the hood yet, but it doesn't look like you can grab multiple series from FRED data at the moment. This works

```
from pandas.io.data import DataReader

merge = lambda x,y : x.merge(y, left_index=True, right_index=True)
dta = reduce(merge, [DataReader(i, "fred") for i in ["AKUR", "ALUR","GAUR"]])
```

but this just hangs and then returns an empty DataFrame

```
dta = DataReader(["AKUR", "ALUR","GAUR"], "fred")
```
