BUG: python 3 compression and read_fwf
Getting a `TypeError: Type str doesn't support the buffer API` when using `read_fwf` on a compressed file with python 3 only; works in python 2.7

Example:

with a file `fwf.bug.txt` like

```
1111111111
2222222222
3333333333
4444444444

```

``` python
import pandas as pd

print(pd.__version__)

widths = [5, 5]

!gzip -d fwf_bug.txt

df = pd.read_fwf('fwf_bug.txt', widths=widths, names=['one', 'two'])
print(df)

!gzip fwf_bug.txt

# python 3 throws an error here.
df2 = pd.read_fwf('fwf_bug.txt.gz', widths=widths,
                  names=['one', 'two'], compression='gzip')

print(df2)
```

Versions:
python3: `0.11.1.dev-4d06037` should be most recent
python2: `0.11.1.dev-3ebfef9`

I can paste the full traceback if you'd like.
