read_csv in multiple theads causes segmentation fault
The following script causes a segfault on my machine

``` python
from io import BytesIO
from multiprocessing.pool import ThreadPool
import pandas as pd

# Make many fake CSV files in memory
bytes = ['\n'.join(['%d,%d,%d' % (i,i,i) for i in range(10000)]).encode()
         for j in range(100)]
files = [BytesIO(b) for b in bytes]

# Read all files in many threads
pool = ThreadPool(8)
pool.map(pd.read_csv, files)
```

```
$ python script.py 
Segmentation fault (core dumped)
```

Python 3.4, Pandas 0.17.1, Ubuntu 14.04
