BUG: regression in Timedelta.__rfloordiv__ with integer data
From a failing example in the docs (http://pandas-docs.github.io/pandas-docs-travis/timeseries.html#from-timestamps-to-epoch):

```
In [46]: stamps = pd.date_range('2012-10-08 18:15:05', periods=4, freq='D')

In [47]: stamps.view('int64') // pd.Timedelta(1, unit='s')
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-47-9893b9bae6cf> in <module>()
----> 1 stamps.view('int64') // pd.Timedelta(1, unit='s')

/home/joris/scipy/pandas/pandas/_libs/tslibs/timedeltas.pyx in pandas._libs.tslibs.timedeltas.Timedelta.__rfloordiv__()

TypeError: Invalid dtype int64 for __floordiv__
```

This was working correctly in 0.22, and is mentioned in the docs explicitly as a way to get unix epoch data.

The previously working example (http://pandas.pydata.org/pandas-docs/stable/timeseries.html#from-timestamps-to-epoch) looks like:

```
In [42]: stamps.view('int64') // pd.Timedelta(1, unit='s')
Out[42]: array([1349720105, 1349806505, 1349892905, 1349979305])
```

cc @jbrockmendel 