BUG: Error in gbq.py
Hi,

``` python
from  pandas.io import gbq
```

 gives the following error:

``` python
>>> from  pandas.io import gbq
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/site-packages/pandas/__init__.py", line 45, in <module>
    from pandas.io.api import *
  File "/usr/local/lib/python2.7/site-packages/pandas/io/api.py", line 15, in <module>
    from pandas.io.gbq import read_gbq
  File "/usr/local/lib/python2.7/site-packages/pandas/io/gbq.py", line 39, in <module>
    if LooseVersion(_GOOGLE_API_CLIENT_VERSION >= '1.2.0'):
  File "/usr/local/Cellar/python/2.7.8_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/version.py", line 265, in __init__
    self.parse(vstring)
  File "/usr/local/Cellar/python/2.7.8_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/version.py", line 274, in parse
    self.component_re.split(vstring))
TypeError: expected string or buffer
```

The error is in [gbq.py](https://github.com/pydata/pandas/blob/master/pandas/io/gbq.py) line 46:

``` python
if LooseVersion(_GOOGLE_API_CLIENT_VERSION >= '1.2.0'):
```

Correct this to:

``` python
if LooseVersion(_GOOGLE_API_CLIENT_VERSION) >= '1.2.0':
```

to return true when the google api client has the correct version.
