BUG: Timedelta repr doesn't show nano
xref #9309, though that's about consistency, not just missing info.

```python
In [7]: pd.Timedelta(nanoseconds=1)
Out[7]: Timedelta('0 days 00:00:00.000000')

In [8]: pd.Timestamp("2000-01-01")-pd.Timedelta(nanoseconds=1)
Out[8]: Timestamp('1999-12-31 23:59:59.999999999')
```

@jorisvandenbossche, recall we discussed using "roles" for repr? this might be a good use case, considering https://github.com/pandas-dev/pandas/issues/9309#issuecomment-70958154.
