BUG: fix hash collisions for from int overflow
hash collisions brought up: https://github.com/pandas-dev/pandas/issues/14711#issuecomment-264885726


closes #14804 

thanks team!

cc @mrocklin
cc @mikegraham  ## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/14805?src=pr) is 85.27% (diff: 100%)
> Merging [#14805](https://codecov.io/gh/pandas-dev/pandas/pull/14805?src=pr) into [master](https://codecov.io/gh/pandas-dev/pandas/branch/master?src=pr) will increase coverage by **<.01%**

```diff
@@             master     #14805   diff @@
==========================================
  Files           144        144          
  Lines         50953      50953          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43451      43452     +1   
+ Misses         7502       7501     -1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [53bf1b2...707becf](https://codecov.io/gh/pandas-dev/pandas/compare/53bf1b27c7dac2a8d72d9bcfe75f514dae8e8c96...707becfc8bf0d5d8ac615696037b03300d5f65b1?src=pr)