BUG: np.round does not work on a series in 0.18.0
First, `conda install pandas` is currently pulling down 0.18.0, which was unexpected since I only see RCs right now, but, on to the real issue...

In 0.18.0 I cannot pass a series to np.round...

``` python
In [35]: np.round(pd.Series([1.11, 2.21]), 1)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-35-4cc66a785b99> in <module>()
----> 1 np.round(pd.Series([1.11, 2.21]), 1)

/Users/holmgren/miniconda3/envs/pvlib35/lib/python3.5/site-packages/numpy/core/fromnumeric.py in round_(a, decimals, out)
   2784     except AttributeError:
   2785         return _wrapit(a, 'round', decimals, out)
-> 2786     return round(decimals, out)
   2787
   2788

TypeError: round() takes from 1 to 2 positional arguments but 3 were given
```

np.round does still work on a DataFrame in 0.18.0...

``` python
In [5]: np.round(pd.DataFrame([1.11,2.22]), 1)
Out[5]:
     0
0  1.1
1  2.2
```

A Series on pandas 0.17.1...

``` python
In [4]: np.round(pd.Series([1.12, 2.22]), 1)
Out[4]:
0    1.1
1    2.2
dtype: float64
```

Ok, I know that there's now a round method in pandas (which is great), but I like to use np.round in unit tests so that I can test against earlier versions of pandas. 

Version info:

``` python
In [34]: pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.5.1.final.0
python-bits: 64
OS: Darwin
OS-release: 15.3.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.18.0
nose: 1.3.7
pip: 8.1.0
setuptools: 20.2.2
Cython: None
numpy: 1.10.4
scipy: 0.17.0
statsmodels: None
xarray: None
IPython: 4.1.1
sphinx: 1.3.5
patsy: None
dateutil: 2.4.2
pytz: 2015.7
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
```
