DOC: warnings with new panel apply functionality
@jreback related to #5850 

There are two warnings remaining in the doc building, both coming from new `panel.apply` functionality:

```
>>>-------------------------------------------------------------------------
Warning in source/v0.13.1.txt at block ending on line 142
----------------------------------------------------------------------------
/home/joris/scipy/pandas/pandas/core/frame.py:2805: FutureWarning: TimeSeries
broadcasting along DataFrame index by default is deprecated. Please use
DataFrame.<op> to explicitly broadcast arithmetic operations along the index
FutureWarning)
<<<-------------------------------------------------------------------------
```

```
>>>-------------------------------------------------------------------------
Warning in /home/joris/scipy/pandas/doc/source/basics.rst at block ending on line 735
----------------------------------------------------------------------------
/home/joris/scipy/pandas/pandas/core/frame.py:2805: FutureWarning: TimeSeries
broadcasting along DataFrame index by default is deprecated. Please use
DataFrame.<op> to explicitly broadcast arithmetic operations along the index
FutureWarning)
<<<-------------------------------------------------------------------------
```
