'Series' object has no attribute 'items' on Python 2.7
#### Code Sample, a copy-pastable example if possible

Running on the REPL with Python 2.7:

```python
Python 2.7.13 |Continuum Analytics, Inc.| (default, Dec 20 2016, 23:05:08)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
Anaconda is brought to you by Continuum Analytics.
Please check out: http://continuum.io/thanks and https://anaconda.org
>>> import pandas as pd
>>> s = pd.Series([1, 2, 3])
>>> for _, x in s.items():
...     print(x)
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/depalati/miniconda3/envs/py27/lib/python2.7/site-packages/pandas/core/generic.py", line 2966, in __getattr__
    return object.__getattribute__(self, name)
AttributeError: 'Series' object has no attribute 'items'
```

On Python 3.6:

```python
Python 3.6.2 |Continuum Analytics, Inc.| (default, Jul 20 2017, 13:14:59)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas as pd
>>> s = pd.Series([1, 2, 3])
>>> for _, x in s.items():
...     print(x)
...
1
2
3
>>>
```

#### Problem description

The `Series.items` method is mysteriously absent on Python 2.7, though `Series.iteritems` works fine on both legacy and modern Python.

#### Expected Output

`Series.items` should iterate over (index, value) tuples.

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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.13.final.0
python-bits: 64
OS: Darwin
OS-release: 16.0.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: None.None

pandas: 0.20.3
pytest: 3.2.1
pip: 9.0.1
setuptools: 27.2.0
Cython: None
numpy: 1.11.3
scipy: 0.18.1
xarray: None
IPython: 5.1.0
sphinx: None
patsy: None
dateutil: 2.6.0
pytz: 2017.2
blosc: None
bottleneck: None
tables: 3.3.0
numexpr: 2.6.1
feather: None
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.9.4
s3fs: None
pandas_gbq: None
pandas_datareader: None

</details>
