Segmentation fault with MultiIndex join()
With pandas from the current master branch and python-3.2.2, I'm getting a seg fault with the following minimal example:

```
df1 = pandas.DataFrame({'a': [1, 1], 'b': [1, 2], 'x': [1, 2]})
df2 = pandas.DataFrame({'a': [2, 2], 'b': [1, 2], 'y': [1, 2]})
df1 = df1.set_index(['a', 'b'])
df2 = df2.set_index(['a', 'b'])
df1.join(df2)

Process Python segmentation fault
```
