COMPAT: boto import issues
@TomAugspurger any progress on #11915 

for `boto` to release a broken version is really annoying.
 @TomAugspurger I just moved this all to a better location which at worse case would only raise on actual s3 import, rather than at pandas import time. I think this will also make integrating via s3fs slightly easier.

lmk.
 K, rebasing on those changes is `test_parser.py` right now. I think I was pretty close to having it working. Will put up a PR this morning.
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13136?src=pr) is **84.14%**

> Merging [#13136](https://codecov.io/gh/pydata/pandas/pull/13136?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **+<.01%**

``` diff
@@             master     #13136   diff @@
==========================================
  Files           137        137          
  Lines         50287      50285     -2   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          42312      42311     -1   
+ Misses         7975       7974     -1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [43989fd...75e3ef1](https://codecov.io/gh/pydata/pandas/compare/43989fd7cb9917e885c2b55a172c4f9f3838d59d...75e3ef15e144a6cf2dd7dbe83a24311a96d7a081)
 I have revised a bit. certainly ok with you making whatever changes, just want to get this out of the main import path.
 @TomAugspurger any issue with this reorg? (I think your PR should easily go on top of this). hopefully can add more test coverage :)
 Yeah, +1 on this I think.
 @TomAugspurger gr8. 
