API: Preserve int columns in to_dict('index')
- [x] closes #18580
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @reidy-p! Thanks for updating the PR.





Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on March 22, 2018 at 19:31 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20444?src=pr&el=h1) Report
> Merging [#20444](https://codecov.io/gh/pandas-dev/pandas/pull/20444?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/02477dab1e4dfb26597806899f8ebf2ca019c30a?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20444/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/20444?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #20444   +/-   ##
=======================================
  Coverage    91.8%    91.8%           
=======================================
  Files         152      152           
  Lines       49223    49223           
=======================================
  Hits        45191    45191           
  Misses       4032     4032
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.19% <100%> (ø)` | :arrow_up: |
| #single | `41.84% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20444?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/20444/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.18% <100%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20444?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/20444?src=pr&el=footer). Last update [02477da...16e1a08](https://codecov.io/gh/pandas-dev/pandas/pull/20444?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 lgtm. just want to make sure windows passes. ping on green. @jreback it's green now. Thanks! thanks @reidy-p keep em coming!