BUG: segfault with .loc indexing
I found that segfault that messed up my HDFStore earlier.

You'll need to csv files:

https://www.dropbox.com/s/55gcpkp3b8byfka/df1.csv
https://www.dropbox.com/s/mqqhfgocdg4qggp/df2.csv

To reproduce:

``` python
In [1]: df1 = pd.read_csv('df1.csv', index_col=[0,1,2])

In [2]: df2 = pd.read_csv('df2.csv', index_col=[0,1,2])

In [3]: df2.loc[df1.index]
Segmentation fault: 11
(pandas-dev)dhcp80fff527:Desktop tom$ 
```

I've never debugged a segfault before, but I gather there are some [methods](https://wiki.python.org/moin/DebuggingWithGdb).  Can anyone reproduce this?

Also, that's a valid use of `.loc` right?

In [1]: pd.**version**
Out[1]: '0.12.0-1084-ged64416'

In [2]: np.**version**
Out[2]: '1.7.1'
