BUG: Fix for .extractall (single group with quantifier) #13382
- [X] closes #13382
- [X] tests added / passed
- [X] passes `git diff upstream/master | flake8 --diff`
- [X] whatsnew entry

Note that I had to fix it based on this [thread](http://stackoverflow.com/questions/2111759/whats-the-best-practice-for-handling-single-value-tuples-in-python), rather than directly with `[x for x in ['ab']]` as this broke previous tests. 
