Crash in DataFrame.reindex
Not sure if it's a bug or just me doing something wrong, but the code below crashes after about two seconds of 100% CPU utilization:

```
from pandas import DataFrame
df = DataFrame({'a': [1, 2, 3], 'b': [4, 5, 6]})
df2 = DataFrame({'c': [2, 2], 'd': [3, 3]})
gp2 = df2.groupby('c')['d']
df.reindex(gp2.index)

ERROR: An unexpected error occurred while tokenizing input
The following traceback may be corrupted or invalid
The error message is: ('EOF in multi-line statement', (2494, 0))
[...]
TypeError: unhashable type: 'numpy.ndarray'
```
