Period slicing with period_range returns error
Slicing a TimeSeries object with a PeriodIndex fails with an index out of bounds error

Example

dates = pd.period_range(start='01-Apr-11',end='31-Mar-12 23:00',freq='h')
ts = pd.TimeSeries(0,dates)
ts[ts.index[4:10]]

Traceback (most recent call last):

  File "<ipython-input-2-c28eee792d28>", line 3, in <module>
    ts[ts.index[4:10]]

  File "C:\dev\bin\Python27\lib\site-packages\pandas\core\series.py", line 506, in **getitem**
    return self._get_with(key)

  File "C:\dev\bin\Python27\lib\site-packages\pandas\core\series.py", line 544, in _get_with
    return self._get_values(key)

  File "C:\dev\bin\Python27\lib\site-packages\pandas\core\series.py", line 575, in _get_values
    return self.values[indexer]

IndexError: index 361564 out of bounds 0<=index<8784

It appears the PeriodIndex is being inferred as 'integer' in series._get_with() using lib.infer_dtype() whereas self.index.inferred_type returns 'period'

```
        if isinstance(key, Index):
            key_type = lib.infer_dtype(key.values)
        else:
            key_type = lib.infer_dtype(key)

        if key_type == 'integer':
            if self.index.inferred_type == 'integer':
                return self.reindex(key)
            else:
                return self._get_values(key)
        elif key_type == 'boolean':
            return self._get_values(key)
```
