ER: Bug accessing a series MultiIndex with a Timestamp
I have a series with a multiindex (datetime, int).
When I try to access a slice corresponding to a date using a Timestamp I have an exception printed to screen if the size of the series is >= 1e6.
No problem if I access the same slice with a string.
No problem with an equivalent dataframe.
Tested on 0.10.1 and 0.11, I'm sorry but I don't have access to 0.12rc1.

``` python

In [1]: import pandas as pd

In [2]: pd.__version__
Out[2]: '0.11.0'

In [3]: np.__version__
Out[3]: '1.7.1'

In [4]: df = pd.DataFrame(randn(1000, 1000), index=pd.date_range('2000-1-1', periods=1000))

In [5]: s = df.stack() # s has 1e6 lines

In [6]: s.head()
Out[6]:
2000-01-01  0   -0.555228
            1   -0.152952
            2    0.401490
            3   -1.057106
            4   -0.987895
dtype: float64

In [7]: s['2000-1-4'].head()
Out[7]:
0   -1.009647
1    0.094427
2    0.105180
3   -2.166810
4   -0.767165
dtype: float64

In [8]: s[pd.Timestamp('2000-1-4')].head()
Exception TypeError: TypeError('Cannot compare Timestamp with (<Timestamp: 2002-09-26 00:00:00>, 999)',) in 'pandas.index._bin_search' ignored
Out[8]:
0   -1.009647
1    0.094427
2    0.105180
3   -2.166810
4   -0.767165
dtype: float64

In [9]: s2 = s[:-1].copy() # s2 has 1e6 - 1 lines

In [10]: s2['2000-1-4'].head()
Out[10]:
0   -1.009647
1    0.094427
2    0.105180
3   -2.166810
4   -0.767165
dtype: float64

In [11]: s2[pd.Timestamp('2000-1-4')].head()
Out[11]:
0   -1.009647
1    0.094427
2    0.105180
3   -2.166810
4   -0.767165
dtype: float64

In [12]: df2 = pd.DataFrame(s)

In [13]: df2.ix['2000-1-4'].head()
Out[13]:
          0
0 -1.009647
1  0.094427
2  0.105180
3 -2.166810
4 -0.767165

In [14]: df2.ix[pd.Timestamp('2000-1-4')].head()
Out[14]:
          0
0 -1.009647
1  0.094427
2  0.105180
3 -2.166810
4 -0.767165

```
