DataFrame.to_hdf fails in Python 3.4
This may be more of a PyTables issue but it affects Pandas users too

``` Python
>>> import pandas as pd
>>> df = pd.DataFrame({'a': [1, 2, 3]})
>>> df.to_hdf('myfile.hdf5', '/data', append=True)
  File "/home/mrocklin/Software/anaconda/envs/py34/lib/python3.4/site-packages/tables/attributeset.py", line 381, in _g__setattr
    elif name == "FILTERS" and self._v__format_version >= (2, 0):
TypeError: unorderable types: NoneType() >= tuple()
```

It appears that `self._v__format_version is None`.  Not sure why.

``` Python
>>> import sys
>>> sys.version
'3.4.2 |Anaconda 2.1.0 (64-bit)| (default, Oct 21 2014, 17:16:37) \n[GCC 4.4.7 20120313 (Red Hat 4.4.7-1)]'
>>> pd.__version__
'0.14.1'
>>> import tables
>>> tables.__version__
'3.1.1'
```

This works fine with `append=False`

``` Python
>>> df.to_hdf('myfile.hdf5', '/data', append=False)
>>> 
```
