BUG: assert_index_equal does not raise error for check_categorical=False when comparing 2 CategoricalIndex objects
- [x] closes #19776 
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

* tests added for `check_categorical` parameter in `assert_series_equal`
* cleaned up `assert_categorical_equal` parameter order and docstring to match other functions (`obj` at the end)

Thanks to all maintainers who helped answer questions on Gitter during the informal PyCon sprint!
Hello @alysivji! Thanks for updating the PR.





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

##### Comment last updated on May 17, 2018 at 13:21 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21092?src=pr&el=h1) Report
> Merging [#21092](https://codecov.io/gh/pandas-dev/pandas/pull/21092?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/501f0418c00064f5041ef156ed5a2289a9064da3?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21092/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/21092?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21092      +/-   ##
==========================================
+ Coverage   91.83%   91.84%   +<.01%     
==========================================
  Files         153      153              
  Lines       49495    49498       +3     
==========================================
+ Hits        45454    45459       +5     
+ Misses       4041     4039       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <100%> (ø)` | :arrow_up: |
| #single | `41.88% <100%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21092?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/21092/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `84.81% <100%> (+0.21%)` | :arrow_up: |
| [pandas/core/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/21092/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYmFzZS5weQ==) | `96.83% <0%> (ø)` | :arrow_up: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/21092/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.23% <0%> (ø)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21092?src=pr&el=footer). Last update [501f041...86999e3](https://codecov.io/gh/pandas-dev/pandas/pull/21092?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @alysivji 