DOC: warnings with new panel apply functionality

[jorisvandenbossche]

@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
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/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
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/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)
<<<-------------------------------------------------------------------------