Fix rfloordiv return type, un-xfail Timedelta tests
- [ ] closes #xxxx
- [x] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19820?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@b585e3b`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19820/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/19820?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #19820   +/-   ##
=========================================
  Coverage          ?   91.58%           
=========================================
  Files             ?      150           
  Lines             ?    48892           
  Branches          ?        0           
=========================================
  Hits              ?    44780           
  Misses            ?     4112           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.96% <ø> (?)` | |
| #single | `41.79% <ø> (?)` | |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19820?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19820?src=pr&el=footer). Last update [b585e3b...8b2f38e](https://codecov.io/gh/pandas-dev/pandas/pull/19820?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 needs rebase actually. ping on green. thanks