pandas index does not give expected behaviour when raised to a power
#### Code Sample, a copy-pastable example if possible

```python
>>> import pandas as pd
>>> test = list(range(5))
>>> a = pd.Series(test, index=test)
>>> a.index
Int64Index([0, 1, 2, 3, 4], dtype='int64')
>>> 0.5**a.index
Float64Index([0.0, 1.0, 1.41421356237, 1.73205080757, 2.0], dtype='float64')

```
#### Problem description

The index doesn't seem to behave properly when it is being raised to the power. It is not giving the correct values. It seems to work well with other operations like multiplication. 

#### Expected Output
```python
Float64Index(array([ 1.    ,  0.5   ,  0.25  ,  0.125 ,  0.0625]), dtype='float64')
```

#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 78 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.19.2
nose: None
pip: 9.0.1
setuptools: 27.2.0
Cython: None
numpy: 1.11.3
scipy: 0.18.1
statsmodels: None
xarray: 0.9.1
IPython: 5.1.0
sphinx: None
patsy: None
dateutil: 2.6.0
pytz: 2016.10
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.3
openpyxl: None
xlrd: 1.0.0
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.9.4
boto: None
pandas_datareader: None
</details>
