Improper handling of Series in Series constructor
This looks like a regression that did not have a unit test (pretty sure this used to do the right thing)

```
index1 = ['d', 'b', 'a', 'c']
index2 = sorted(index1)
s1 = Series([4, 7, -5, 3], index=index1)
s2 = Series(s1, index=index2)
```

cc @hughdbrown
