Segfault with pd.tslib.get_period_field FIX
closes #4519

@prossahl
pls do 1 pr per issue
create a new tracking branch off of current master to keep them separate
 do 

```
git checkout thisbranch
git checkout -b newbranch
git rebase -i <commit before 1211711>``
git push myfork newbranch
```

and delete the first 2 commits; this makes this branch independent
 Abandoned. I'll resubmit this.
 @prossahl should this be closed then?
 @cpcloud Well without the change the segfault can still happen. I'll submit a new pull request as this one pulled in irrelevant changes.
 you don't need to do that. do this

``` sh
git reset HEAD~1
git stash
git fetch upstream
git reset --hard upstream/master
git stash pop
git commit -am'Your awesome commit message'
git push --force
```
 Thanks v. much for your help but its a no go.
git stash  results in "No local changes to save". git fetch upstream results in "fatal: 'upstream' does not appear to be a git repository"
I think that my git repo is so messed up it will be quicker to create a new account and start from the beginning...
 check out this wiki page:

https://github.com/pydata/pandas/wiki/Using-Git

and also pls read this:

https://github.com/pydata/pandas/blob/master/CONTRIBUTING.md
