column multiindex and reindex inconsistency 
```python
In [3]: df1 = pd.DataFrame(np.random.randint(0,10,(4,3)), columns=['a','b','c'])

In [4]: df1
Out[4]: 
   a  b  c
0  9  3  2
1  9  0  2
2  7  7  6
3  3  4  2

In [5]: df2 = df1.reindex(columns=['c','a','d'])

In [6]: df2
Out[6]: 
   c  a   d
0  2  9 NaN
1  2  9 NaN
2  6  7 NaN
3  2  3 NaN

In [7]: df2.columns
Out[7]: Index([u'c', u'a', u'd'], dtype='object')

In [8]: ci = pd.MultiIndex.from_product([['x','y'],['a','b','c']])

In [10]: df3 = pd.DataFrame(np.random.randint(0,10,(4,6)), columns=ci)

In [11]: df3
Out[11]: 
   x        y      
   a  b  c  a  b  c
0  3  1  5  3  8  7
1  2  7  6  8  7  4
2  8  3  5  7  1  1
3  7  5  8  7  8  7

In [12]: df4 = df3.reindex(columns=['c','a','d'], level=1)

In [13]: df4
Out[13]: 
   x     y   
   c  a  c  a
0  5  3  7  3
1  6  2  4  8
2  5  8  1  7
3  8  7  7  7

In [14]: df4.columns
Out[14]: 
MultiIndex(levels=[[u'x', u'y'], [u'c', u'a', u'd']],
           labels=[[0, 0, 1, 1], [0, 1, 0, 1]])
```

When passing a _nonexistent_ column name to `reindex` on a dataframe without multiindex columns, the result is:
- a `NaN` column with the "new" column name
- the `columns` attribute matches the columns in the dataframe

The same action on a multiindex dataframe produces different results:
- there are no `NaN` columns (this may not be a problem)
- the `columns` attribute of the resulting dataframe does not match the dateframe column names  (this appears to be a bug)

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Darwin
OS-release: 16.3.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: None.None

pandas: 0.19.1
nose: 1.3.7
pip: 9.0.1
setuptools: 27.2.0
Cython: 0.25.1
numpy: 1.11.2
scipy: 0.18.1
statsmodels: 0.6.1
xarray: None
IPython: 5.1.0
sphinx: 1.4.8
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2016.7
blosc: None
bottleneck: 1.1.0
tables: 3.3.0
numexpr: 2.6.1
matplotlib: 1.5.3
openpyxl: 2.4.0
xlrd: 1.0.0
xlwt: 1.1.2
xlsxwriter: 0.9.3
lxml: 3.6.4
bs4: 4.5.1
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.1.4
pymysql: None
psycopg2: 2.6.2 (dt dec pq3 ext lo64)
jinja2: 2.8
boto: 2.43.0
pandas_datareader: None

</details>
