DEPR: remove warning / suppress if indexes are equal
https://github.com/pydata/pandas/issues/6087

I have to investigate more fully, but this warning

`/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)`

can be removed for cases where the index are equal (e.g. no broadcasting)
