API: restore full datetime.timedelta compat with Timedelta w.r.t. seconds/microseconds accessors (GH9185, GH9139)
closes #9185
closes #9139 

@shoyer @jorisvandenbossche 

I think this should bring us back to the previous behavior.
 I think we also need to update the timedelta docs: http://pandas.pydata.org/pandas-docs/stable/timedeltas.html
 all comments have been addressed.
 OK, looks good to me!
 Thanks Jeff!
