msgpack file created with 0.16 cannot be read in 0.20.3: UnicodeDecodeError
#### Problem description

I have several msgpack encoded data frames from old versions of pandas. I have seen the warnings about this format. However, it seems there are some tests that ensure that old versions can still be loaded. For the current master that seems to include also pandas version 0.16. [This](https://github.com/pandas-dev/pandas/files/1600428/data.zip) is a file that was created with 0.16, which cannot be loaded in 0.20.3.

This is what happens when trying to load the file:
```
In [4]: pd.read_msgpack('/home/languitar/data/tobi-dataset-post-processed/1/armcontrol-features-Combined+hash.msg')
---------------------------------------------------------------------------
UnicodeDecodeError                        Traceback (most recent call last)
<ipython-input-4-8e36ed25a239> in <module>()
----> 1 pd.read_msgpack('/home/languitar/data/tobi-dataset-post-processed/1/armcontrol-features-Combined+hash.msg')

/home/languitar/miniconda2/envs/monitoring/lib/python2.7/site-packages/pandas/io/packers.pyc in read_msgpack(path_or_buf, encoding, iterator, **kwargs)
    201         if exists:
    202             with open(path_or_buf, 'rb') as fh:
--> 203                 return read(fh)
    204 
    205     # treat as a binary-like

/home/languitar/miniconda2/envs/monitoring/lib/python2.7/site-packages/pandas/io/packers.pyc in read(fh)
    186 
    187     def read(fh):
--> 188         l = list(unpack(fh, encoding=encoding, **kwargs))
    189         if len(l) == 1:
    190             return l[0]

pandas/io/msgpack/_unpacker.pyx in pandas.io.msgpack._unpacker.Unpacker.__next__ (pandas/io/msgpack/_unpacker.cpp:5618)()

pandas/io/msgpack/_unpacker.pyx in pandas.io.msgpack._unpacker.Unpacker._unpack (pandas/io/msgpack/_unpacker.cpp:4602)()

UnicodeDecodeError: 'utf8' codec can't decode byte 0xf8 in position 6: invalid start byte
```

#### Expected Output

It should load the data without an exception.

#### Output of ``pd.show_versions()`` for the creating pandas version

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.13.final.0
python-bits: 64
OS: Linux
OS-release: 4.14.6-1-ARCH
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.16.2
nose: None
Cython: None
numpy: 1.10.4
scipy: 0.17.1
statsmodels: 0.6.1
IPython: 5.3.0
sphinx: None
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
bottleneck: None
tables: 3.2.2
numexpr: 2.5.2
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.9999999
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
</details>

#### Output of ``pd.show_versions()`` for the version trying to load the file

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.13.final.0
python-bits: 64
OS: Linux
OS-release: 4.14.9-1-ARCH
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.utf8
LOCALE: None.None

pandas: 0.20.3
pytest: 3.2.1
pip: 9.0.1
setuptools: 36.4.0
Cython: None
numpy: 1.13.1
scipy: 0.19.1
xarray: None
IPython: 5.3.0
sphinx: None
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: None
tables: 3.4.2
numexpr: 2.6.2
feather: None
matplotlib: 2.0.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.9999999
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
pandas_gbq: None
pandas_datareader: None
</details>

  