recursion limit reached when joining period and datetimeindexes
one should probably _not_ be trying to join these types of indices. even so, a stack overflow is unacceptable. there should at least be an error message...

code:

```
In [9]: df = mkdf(10, 10, data_gen_f=lambda *args: randint(2), c_idx_type='p', r_idx_type='dt')

In [10]: s = df.iloc[:5, 0]

In [11]: s.index.join(df.columns, how='outer')
```
