Dataframe constructor fails when given dict with None value
#### A small, complete example of the issue

``` python
# Your code here

import pandas as pd
pd.Dataframe(dict(a=None), index= [0])
```

```
In [3]: pd.DataFrame(dict(a=None),index=[0])
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-3-20b65f605ca3> in <module>()
----> 1 pd.DataFrame(dict(a=None),index=[0])

miniconda2/envs/readout2/lib/python2.7/site-packages/pandas/core/frame.pyc in __init__(self, data, index, columns, dtype, copy)
    264                                  dtype=dtype, copy=copy)
    265         elif isinstance(data, dict):
--> 266             mgr = self._init_dict(data, index, columns, dtype=dtype)
    267         elif isinstance(data, ma.MaskedArray):
    268             import numpy.ma.mrecords as mrecords

miniconda2/envs/readout2/lib/python2.7/site-packages/pandas/core/frame.pyc in _init_dict(self, data, index, columns, dtype)
    400             arrays = [data[k] for k in keys]
    401 
--> 402         return _arrays_to_mgr(arrays, data_names, index, columns, dtype=dtype)
    403 
    404     def _init_ndarray(self, values, index, columns, dtype=None, copy=False):

miniconda2/envs/readout2/lib/python2.7/site-packages/pandas/core/frame.pyc in _arrays_to_mgr(arrays, arr_names, index, columns, dtype)
   5382 
   5383     # don't force copy because getting jammed in an ndarray anyway
-> 5384     arrays = _homogenize(arrays, index, dtype)
   5385 
   5386     # from BlockManager perspective

miniconda2/envs/readout2/lib/python2.7/site-packages/pandas/core/frame.pyc in _homogenize(data, index, dtype)
   5693                 v = lib.fast_multiget(v, oindex.values, default=NA)
   5694             v = _sanitize_array(v, index, dtype=dtype, copy=False,
-> 5695                                 raise_cast_failure=False)
   5696 
   5697         homogenized.append(v)

miniconda2/envs/readout2/lib/python2.7/site-packages/pandas/core/series.pyc in _sanitize_array(data, index, dtype, copy, raise_cast_failure)
   2917 
   2918     # scalar like
-> 2919     if subarr.ndim == 0:
   2920         if isinstance(data, list):  # pragma: no cover
   2921             subarr = np.array(data, dtype=object)

AttributeError: 'NoneType' object has no attribute 'ndim'
```
#### Expected Output

This previously worked with a sensible output in 0.18.1:

In [2]: pd.DataFrame(dict(a=None),index=[0])
Out[2]: 
      a
0  None
#### Output of `pd.show_versions()`

<details>
Working version:
## INSTALLED VERSIONS

commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Linux
OS-release: 3.2.0-4-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.18.1
nose: 1.3.7
pip: 8.1.2
setuptools: 27.2.0
Cython: 0.24
numpy: 1.11.2
scipy: 0.17.0
statsmodels: 0.6.1
xarray: None
IPython: 4.2.0
sphinx: 1.4.1
patsy: 0.4.1
dateutil: 2.5.3
pytz: 2016.7
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.4.4
matplotlib: 1.5.1
openpyxl: 2.3.2
xlrd: 0.9.4
xlwt: 1.0.0
xlsxwriter: 0.8.5
lxml: 3.6.0
bs4: 4.3.2
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.12
pymysql: None
psycopg2: None
jinja2: 2.8
boto: 2.39.0
pandas_datareader: None

Broken version:
## INSTALLED VERSIONS

commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Linux
OS-release: 3.2.0-4-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: None.None

pandas: 0.19.0
nose: 1.3.7
pip: 8.1.2
setuptools: 27.2.0
Cython: 0.24
numpy: 1.11.2
scipy: 0.17.0
statsmodels: 0.6.1
xarray: None
IPython: 4.2.0
sphinx: 1.4.1
patsy: 0.4.1
dateutil: 2.5.3
pytz: 2016.7
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.4.4
matplotlib: 1.5.1
openpyxl: 2.3.2
xlrd: 0.9.4
xlwt: 1.0.0
xlsxwriter: 0.8.5
lxml: 3.6.0
bs4: 4.3.2
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.12
pymysql: None
psycopg2: None
jinja2: 2.8
boto: 2.39.0
pandas_datareader: None

</details>
