Indexing by a list of Periods fails to return a series
```
In [1]: import pandas as pd

In [2]: pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.7.final.0
python-bits: 32
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 30 Stepping 5, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.14.0
nose: 1.3.3
Cython: 0.20.2
numpy: 1.8.1
scipy: 0.14.0
statsmodels: 0.5.0
IPython: 2.1.0
sphinx: 1.2.2
patsy: 0.2.1
scikits.timeseries: None
dateutil: 1.5
pytz: 2014.4
bottleneck: None
tables: 3.1.1
numexpr: 2.3.1
matplotlib: 1.3.1
openpyxl: 1.8.5
xlrd: 0.9.3
xlwt: 0.7.5
xlsxwriter: 0.5.5
lxml: 3.3.5
bs4: 4.3.1
html5lib: 0.999
bq: None
apiclient: None
rpy2: 2.3.9
sqlalchemy: 0.9.4
pymysql: None
psycopg2: 2.5.3 (dt dec pq3 ext)

In [3]: s = pd.TimeSeries(1, [pd.Period('2002-01-01',freq='D')])

In [4]: s[[0]]
Out[4]:
2002-01-01    1
Freq: D, dtype: int64

In [5]: s[[pd.Period('2002-01-01',freq='D')]]
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-5-0e636383b52c> in <module>()
----> 1 s[[pd.Period('2002-01-01',freq='D')]]

C:\Python27\lib\site-packages\pandas\core\series.pyc in __getitem__(self, key)
    517             key = _check_bool_indexer(self.index, key)
    518
--> 519         return self._get_with(key)
    520
    521     def _get_with(self, key):

C:\Python27\lib\site-packages\pandas\core\series.pyc in _get_with(self, key)
    555                     # handle the dup indexing case (GH 4246)
    556                     if isinstance(key, (list, tuple)):
--> 557                         return self.ix[key]
    558
    559                     return self.reindex(key)

C:\Python27\lib\site-packages\pandas\core\indexing.pyc in __getitem__(self, key)
     68             return self._getitem_tuple(key)
     69         else:
---> 70             return self._getitem_axis(key, axis=0)
     71
     72     def _get_label(self, label, axis=0):

C:\Python27\lib\site-packages\pandas\core\indexing.pyc in _getitem_axis(self, key, axis, validate_iterable)
    849                 raise ValueError('Cannot index with multidimensional key')
    850
--> 851             return self._getitem_iterable(key, axis=axis)
    852         else:
    853             if com.is_integer(key):

C:\Python27\lib\site-packages\pandas\core\indexing.pyc in _getitem_iterable(self, key, axis)
    905             # existing labels are unique and indexer is unique
    906             if labels.is_unique and keyarr_is_unique:
--> 907                 return _reindex(keyarr, level=level)
    908
    909             else:

C:\Python27\lib\site-packages\pandas\core\indexing.pyc in _reindex(keys, level)
    875                 if axis != 0:
    876                     raise AssertionError('axis must be 0')
--> 877                 return self.obj.reindex(keys, level=level)
    878
    879         if com._is_bool_indexer(key):

C:\Python27\lib\site-packages\pandas\core\series.pyc in reindex(self, index, **kwargs)
   2026     @Appender(generic._shared_docs['reindex'] % _shared_doc_kwargs)
   2027     def reindex(self, index=None, **kwargs):
-> 2028         return super(Series, self).reindex(index=index, **kwargs)
   2029
   2030     def reindex_axis(self, labels, axis=0, **kwargs):

C:\Python27\lib\site-packages\pandas\core\generic.pyc in reindex(self, *args, **kwargs)
   1608         # if indicated must have index names equal here as well as values
   1609         if all([self._get_axis(axis).identical(ax)
-> 1610                 for axis, ax in axes.items() if ax is not None]):
   1611             if copy:
   1612                 return self.copy()

C:\Python27\lib\site-packages\pandas\core\index.pyc in identical(self, other)
    849         also equal
    850         """
--> 851         return (self.equals(other) and
    852                 all((getattr(self, c, None) == getattr(other, c, None)
    853                      for c in self._comparables)) and

C:\Python27\lib\site-packages\pandas\tseries\period.pyc in equals(self, other)
    822             return True
    823
--> 824         return np.array_equal(self.asi8, other.asi8)
    825
    826     def tolist(self):

AttributeError: 'numpy.ndarray' object has no attribute 'asi8'

```
