WARN: warnings on dateoffse & timedelta arithmetic
```
pandas/tests/series/test_operators.py::TestTimedeltaSeriesArithmetic::()::test_timedelta64_operations_with_DateOffset
  /Users/jreback/pandas/pandas/core/indexes/timedeltas.py:438: PerformanceWarning: Adding/subtracting array of DateOffsets to <class 'pandas.core.indexes.timedeltas.TimedeltaIndex'> not vectorized
    PerformanceWarning)

-- Docs: http://doc.pytest.org/en/latest/warnings.html
======================================================================================= 290 passed, 9 xfailed, 15 xpassed, 1 warnings in 2.37 seconds =======================================================================================
```

@jbrockmendel is this expected? if so should be explicitly caught