pd.Series.count(pd.Index(range(5))) works in python 3 but not python 2.
``` python
In [1]: import pandas as pd

In [2]: i = pd.Index(range(10))

In [3]: pd.Series.count(i)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-759ac5e97e30> in <module>()
----> 1 pd.Series.count(i)

TypeError: unbound method count() must be called with Series instance as first argument (got Int64Index instance instead)

In [4]: pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.10.final.0
python-bits: 64
OS: Linux
OS-release: 4.0.0-2-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.utf8

pandas: 0.16.1
nose: 1.3.6
Cython: None
numpy: 1.9.2
scipy: 0.15.1
statsmodels: None
IPython: 3.1.0
sphinx: 1.2.3
patsy: None
dateutil: 2.4.2
pytz: 2015.4
bottleneck: None
tables: 3.2.0
numexpr: 2.4.3
matplotlib: 1.4.3
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
```
