Series.loc faulty behaviour
### INSTALLED VERSIONS

Python: 2.7.6.final.0
OS: Darwin
Release: 13.0.0
Processor: i386
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.13.0
Cython: 0.19.2
Numpy: 1.8.0
Scipy: 0.13.2
statsmodels: 0.5.0
    patsy: 0.2.0
scikits.timeseries: 0.91.3
dateutil: 2.2
pytz: 2013.8
bottleneck: 0.7.0
PyTables: 2.4.0
    numexpr: 2.2.2
matplotlib: 1.3.1
openpyxl: 1.5.8
xlrd: 0.9.2
xlwt: 0.7.5
xlsxwriter: Not installed
sqlalchemy: 0.8.3
lxml: 3.2.3
bs4: Not installed
html5lib: 0.95-dev
bigquery: Not installed
apiclient: Not installed
### Explanation by use-case:

```
ipdb> !type(self.df)
<class 'pandas.core.frame.DataFrame'>
ipdb> !type(self.df[Column.TRR])
<class 'pandas.core.series.Series'>
ipdb> !type(events_time_axis)
<class 'pandas.core.index.Int64Index'>
ipdb> !type(self.df[Column.TRR].index)
<class 'pandas.core.index.MultiIndex'>
ipdb> !type(events_time_axis[0])
<type 'numpy.int64'>
ipdb> !events_time_axis[0]
120
ipdb> !self.df[Column.TRR].loc[events_time_axis[0]]
*** ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
ipdb> !self.df[Column.TRR].loc[np.int64(events_time_axis[0])]
*** ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
ipdb> !self.df[Column.TRR].loc[int(events_time_axis[0])]
EXTENT
53760      0
192000     1
783360     4
829440     4
...
```

As you see in the last line the workaround was to cast numpy.int64 retrieval from pandas.core.index.Int64Index to int.

```
ipdb> w
  <ipython-input-222-a92c150d8481>(2)<module>()
      1 simulator = FASTSimulator(df, 5, half_life=30 * 12)  # ((30=h)*12)=12 hours)
----> 2 fast_flash_memory_hits, read_requests_at_all = simulator.execute()

> /Users/shkolyar/workspace/python/thesis/simulator.py(82)execute()
     80         current_values_as_zeros = pd.Series(np.zeros_like(extents, np.int),
     81                                             extents)
---> 82         forecast = self.df[Column.TRR].loc[events_time_axis[0]].reindex(
     83             extents, fill_value=0)
     84 

  /Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/indexing.py(1020)__getitem__()
   1018             return self._getitem_tuple(key)
   1019         else:
-> 1020             return self._getitem_axis(key, axis=0)
   1021 
   1022     def _getitem_axis(self, key, axis=0):

  /Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/indexing.py(1145)_getitem_axis()
   1143         else:
   1144             self._has_valid_type(key, axis)
-> 1145             return self._get_label(key, axis=axis)
   1146 
   1147 

  /Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/indexing.py(68)_get_label()
     66             return self.obj._xs(label, axis=axis, copy=False)
     67         except Exception:
---> 68             return self.obj._xs(label, axis=axis, copy=True)
     69 
     70     def _get_loc(self, key, axis=0):

  /Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/series.py(439)_xs()
    437 
    438     def _xs(self, key, axis=0, level=None, copy=True):
--> 439         return self.__getitem__(key)
    440 
    441     xs = _xs

  /Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/series.py(504)__getitem__()
    502                 if type(new_key) != type(key):
    503                     return self.__getitem__(new_key)
--> 504                 raise
    505 
    506         except Exception:

  /Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/index.py(2319)get_value()
   2317                     pass
   2318 
-> 2319             raise InvalidIndexError(key)
   2320 
   2321     def get_level_values(self, level):

  /Users/shkolyar/workspace/HDF5/tmp/index.pyx(416)pandas.index._bin_search (pandas/index.c:7437)()
```
### Stacktrace:

```
     82         forecast = self.df[Column.TRR].loc[events_time_axis[0]].reindex(
     83             extents, fill_value=0)
     84 

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/indexing.pyc in __getitem__(self, key)
   1018             return self._getitem_tuple(key)
   1019         else:
-> 1020             return self._getitem_axis(key, axis=0)
   1021 
   1022     def _getitem_axis(self, key, axis=0):

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/indexing.pyc in _getitem_axis(self, key, axis)
   1143         else:
   1144             self._has_valid_type(key, axis)
-> 1145             return self._get_label(key, axis=axis)
   1146 
   1147 

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/indexing.pyc in _get_label(self, label, axis)
     66             return self.obj._xs(label, axis=axis, copy=False)
     67         except Exception:
---> 68             return self.obj._xs(label, axis=axis, copy=True)
     69 
     70     def _get_loc(self, key, axis=0):

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/series.pyc in _xs(self, key, axis, level, copy)
    437 
    438     def _xs(self, key, axis=0, level=None, copy=True):
--> 439         return self.__getitem__(key)
    440 
    441     xs = _xs

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/series.pyc in __getitem__(self, key)
    482     def __getitem__(self, key):
    483         try:
--> 484             result = self.index.get_value(self, key)
    485             if isinstance(result, np.ndarray):
    486                 return self._constructor(result,index=[key]*len(result)).__finalize__(self)

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/core/index.pyc in get_value(self, series, key)
   2278 
   2279         try:
-> 2280             return self._engine.get_value(s, k)
   2281         except KeyError as e1:
   2282             try:

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/index.so in pandas.index.IndexEngine.get_value (pandas/index.c:2890)()

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/index.so in pandas.index.IndexEngine.get_value (pandas/index.c:2702)()

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/index.so in pandas.index.IndexEngine.get_loc (pandas/index.c:3301)()

/Users/shkolyar/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/index.so in pandas.index._bin_search (pandas/index.c:7437)()

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
```
