BUG/TST: Panel4d comparison operator
pandas.tests.test_panel4d:TestPanel4d. test_setitem fails on 3.x with

``` python
Traceback (most recent call last):

File "/home/travis/virtualenv/python3.1/lib/python3.1/site-packages/pandas-0.10.0.dev_1b7ceed-py3.1-linux-i686.egg/pandas/tests/test_panel4d.py", line 368, in test_setitem

self.panel4d['lP'] = self.panel4d['l1'] > 0

TypeError: unorderable types: Panel() > int()
```

It only passes on 2.x because it's more liberal with respect to bool coercion,
so you get the rather unhelpful:

``` python
In [44]: p['l1']
Out[44]: 
<class 'pandas.core.panel.Panel'>
Dimensions: 3 (items) x 30 (major_axis) x 4 (minor_axis)
Items axis: ItemA to ItemC
Major_axis axis: 2000-01-03 00:00:00 to 2000-02-11 00:00:00
Minor_axis axis: A to D

In [45]: p['l1'] > 1
Out[45]: True
```

Probably not the intended result.
