BUG: DataFrame.consolidate throws TypeError with bytes blocks
#### Code Sample, a copy-pastable example if possible

```python
x = pd.DataFrame([['a']]).astype('S1')
y = pd.concat([x]*2, 1)
y.consolidate()
```
#### Problem description

This throws the following error:

```python
  File "bug.py", line 3, in <module>
    y.consolidate()
  File "/home/anaconda3/lib/python3.5/site-packages/pandas/core/generic.py", line 2822, in consolidate
    cons_data = self._protect_consolidate(f)
  File "/home/anaconda3/lib/python3.5/site-packages/pandas/core/generic.py", line 2790, in _protect_consolidate
    result = f()
  File "/home/anaconda3/lib/python3.5/site-packages/pandas/core/generic.py", line 2821, in <lambda>
    f = lambda: self._data.consolidate()
  File "/home/anaconda3/lib/python3.5/site-packages/pandas/core/internals.py", line 3526, in consolidate
    bm._consolidate_inplace()
  File "/home/anaconda3/lib/python3.5/site-packages/pandas/core/internals.py", line 3531, in _consolidate_inplace
    self.blocks = tuple(_consolidate(self.blocks))
  File "/home/anaconda3/lib/python3.5/site-packages/pandas/core/internals.py", line 4523, in _consolidate
    _can_consolidate=_can_consolidate)
  File "/home/anaconda3/lib/python3.5/site-packages/pandas/core/internals.py", line 4543, in _merge_blocks
    new_values = _vstack([b.values for b in blocks], dtype)
  File "/home/anaconda3/lib/python3.5/site-packages/pandas/core/internals.py", line 4584, in _vstack
    if dtype == _NS_DTYPE or dtype == _TD_DTYPE:
TypeError: data type "bytes8" not understood
```

#### Expected Output

No error should be thrown, y should be consolidated.

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

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Linux
OS-release: 4.9.8-100.fc24.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: C
LANG: C
LOCALE: None.None

pandas: 0.19.2
nose: 1.3.7
pip: 9.0.1
setuptools: 27.2.0
Cython: 0.25.2
numpy: 1.11.3
scipy: 0.18.1
statsmodels: 0.8.0
xarray: 0.9.1
IPython: 4.2.0
sphinx: 1.5.1
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2016.10
blosc: None
bottleneck: 1.2.0
tables: 3.3.0
numexpr: 2.6.2
matplotlib: 2.0.0
openpyxl: 2.4.1
xlrd: 1.0.0
xlwt: 1.2.0
xlsxwriter: 0.9.6
lxml: 3.7.2
bs4: 4.5.3
html5lib: 0.999
httplib2: None
apiclient: None
sqlalchemy: 1.1.5
pymysql: None
psycopg2: None
jinja2: 2.9.4
boto: 2.45.0
pandas_datareader: None
</details>
