Series.reindex() does nothing
#### Code Sample, a copy-pastable example if possible

```python
import numpy as np
import pandas as pd

np.random.seed(42)

nums = np.random.choice(range(0, 999), 1000)
cut = pd.cut(nums, 10)

discretization = cut.value_counts()
discretization.sort_index(inplace=True)

intervals = list(discretization.index)
mids = [i.mid for i in intervals]

print(discretization.reindex(index=mids))
```

Output:

```
(-0.998, 99.8]    100
(99.8, 199.6]     103
(199.6, 299.4]     97
(299.4, 399.2]     94
(399.2, 499.0]     97
(499.0, 598.8]     85
(598.8, 698.6]    118
(698.6, 798.4]    103
(798.4, 898.2]    108
(898.2, 998.0]     95
dtype: int64
```

#### Problem description

`Series.reindex()` returns the original `Series` even though the index is changed.

#### Expected Output

`print(pd.Series(discretization.values, index=mids))` produces:

```
49.401     100
149.700    103
249.500     97
349.300     94
449.100     97
548.900     85
648.700    118
748.500    103
848.300    108
948.100     95
dtype: int64
```

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

<details>

INSTALLED VERSIONS
------------------------
commit: None
python: 3.6.2.final.0
python-bits: 64
OS: Linux
OS-release: 4.9.39-1-MANJARO
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.20.3
pytest: 3.1.3
pip: 9.0.1
setuptools: 36.2.2
Cython: None
numpy: 1.13.1
scipy: 0.19.1
xarray: None
IPython: 5.3.0
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: 1.2.1
tables: None
numexpr: 2.6.2
feather: None
matplotlib: 2.0.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.999999999
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
pandas_gbq: None
pandas_datareader: 0.4.0
</details>
