Have the possibility for Series.unique() to return a Series rather than an array
I admit I haven't looked at the code so there may be reasons for this, but I've found myself in the need of squeezing out duplicates from a Series but keeping the results as a Series.

Series.unique() however returns an array, so in my code I have to construct a Series twice:

``` python

series = pandas.Series([1,2,3,3])
series = pandas.Series(series.unique())
```

Is this by design? If so, feel free to close this bug.
