MultiIndex DataFrame with tuple columns error?
Hi, I am using pandas 0.12.0 and numpy 1.7.1.

I get the below error when storing to a CSV a DataFrame with a multiIndex column composed of tuples and then loading it afterwards.  Thanks for your help!

``` python

import pandas as pd
import numpy as np
tup = ('a','g','b')
arrays = [[tup] * 4, range(1,5)]
tuples = zip(*arrays)
multi_columns = pd.MultiIndex.from_tuples(tuples, names=['first','second'])
index = range(1,10)
df = pd.DataFrame(index = index, columns=multi_columns)
df.to_csv('test.csv', tupleize_cols=False)
df2 = pd.read_csv('test.csv', index_col = 0, parse_dates =  True, header=[0,1], tupleize_cols=False)

df.columns[0][0]
('a', 'g', 'b')
df2.columns[0][0]
"('a', 'g', 'b')"
df2[df.columns[0][0],]

TypeError: not all arguments converted during string formatting
```
