Panel.iloc[] broken
Panel.iloc[] doesn't index correctly given a mix of scalars and ranges

```
from pandas import Panel, date_range
from numpy.random import randn

p = Panel(randn(4, 4, 4))

print(p.iloc[:3, :3, :3].shape)
print(p.iloc[1, :3, :3].shape)
print(p.iloc[:3, 1, :3].shape)
print(p.iloc[:3, :3, 1].shape)
print(p.iloc[1, 1, :3].shape)
print(p.iloc[1, :3, 1].shape)
print(p.iloc[:3, 1, 1].shape)
```

Returns

```
[3, 3, 3]
(4, 3)
(4, 3)
(3, 3)
(3L,)
(4L,)
(4L,)
```
