BUG: DataFrame.to_hdf segfault
```
import pandas as pd

# import dask.dataframe as dd
N = 5000
df = pd.DataFrame({'A': [1, 2] * N, 'B': [3, 4] * N, 'C': ['a', 'b'] * N})

df.to_hdf('foo.h5', '/data', format='table', mode='a')

for _ in range(3):
    df.to_hdf('foo.h5', '/data', format='table', mode='a', append=True)
```

This actually works when `N` is smaller, perhaps something with a pytables chunksize
