Slicing a Panel doesn't work as expected
As discussed in https://groups.google.com/group/pydata/browse_thread/thread/5135792571f99aa4 the following tests fail:

``` python
p = pd.Panel(randint(0, 100, (4,5,2)), 
             pd.date_range('01-Jan-2012', periods=4, freq='MS').shift(15,'D'),
             pd.date_range('01-Jan-2012', periods=5, freq='MS'))
```

``` python
def test_panel_slicing_axis2():
    assert p.ix[:,:,0:1].shape == (4,5,1)
```

``` python
def test_panel_indexing_doesnt_transpose():
    assert  p.ix[:, 1, :].values == p.values[:, 1, :]
    assert p.ix[:, :, 0].values == p.values[:, :, 0]
```
