df.to_hdf() does not support BytesIO
```
In [1]: import io
In [2]: xx = io.BytesIO()
In [4]: from pandas import DataFrame
In [5]: from numpy.random import randn
In [6]: df = DataFrame(randn(1000000,2),columns=list('AB'))

----> 1 df.to_hdf(xx,'xx')

/root/pyenvs/aft_env/lib/python3.4/site-packages/pandas/core/generic.py in to_hdf(self, path_or_buf, key, **kwargs)
    900 
    901         from pandas.io import pytables
--> 902         return pytables.to_hdf(path_or_buf, key, self, **kwargs)
    903 
    904     def to_msgpack(self, path_or_buf=None, **kwargs):

/root/pyenvs/aft_env/lib/python3.4/site-packages/pandas/io/pytables.py in to_hdf(path_or_buf, key, value, mode, complevel, complib, append, **kwargs)
    267             f(store)
    268     else:
--> 269         f(path_or_buf)
    270 
    271 

/root/pyenvs/aft_env/lib/python3.4/site-packages/pandas/io/pytables.py in <lambda>(store)
    260         f = lambda store: store.append(key, value, **kwargs)
    261     else:
--> 262         f = lambda store: store.put(key, value, **kwargs)
    263 
    264     if isinstance(path_or_buf, string_types):

AttributeError: '_io.BytesIO' object has no attribute 'put'
```
