Allow TimeSeries to be initialized using a data vector of type Series
Suppose one has the following data:

``` python
from pandas import Series, TimeSeries, date_range
foo = date_range('2012-1-1', '2012-1-4')
bar = Series(range(0,4))
```

Currently (as of pandas 0.9.1), initializing a `TimeSeries` object using `data` of type `Series` produces unexpected results---all data values are converted to `NaN`.

```
TimeSeries(data = bar, index = foo)

2012-01-01   NaN
2012-01-02   NaN
2012-01-03   NaN
2012-01-04   NaN
Freq: D
```

However, casting the `Series` object to a list produces intuitive results:

```
TimeSeries(data = bar.tolist(), index = foo)

2012-01-01    0
2012-01-02    1
2012-01-03    2
2012-01-04    3
Freq: D
```
