series str as an iterator
This was [noticed on SO](http://stackoverflow.com/questions/16617394/pandas-how-to-select-by-partial-label-in-index/16617491?noredirect=1#comment23892039_16617491) by @DSM. It seems that the Series `str` method is a never ending iterator. I have no idea whether this should be classified as a bug, or just misuse. But here goes:

```
In [224]: g = (i for i in ds.str)

In [225]: next(g)
Out[225]:
google       NaN
wikimedia    NaN
wikipedia    NaN
wikitravel   NaN
dtype: float64

In [226]: next(g)
Out[226]:
google       NaN
wikimedia    NaN
wikipedia    NaN
wikitravel   NaN
dtype: float64

In [227]: next(g)
Out[227]:
google       NaN
wikimedia    NaN
wikipedia    NaN
wikitravel   NaN
dtype: float64

In [228]: next(g)
Out[228]:
google       NaN
wikimedia    NaN
wikipedia    NaN
wikitravel   NaN
dtype: float64

In [229]: list(g)  # lalalala
```
