Add test case for BatPervasives.dump

`BatPervasives.dump` currently produces unexpected output when given (0,0). It will print "[0]" rather than "(0, 0)" as I would've expected.

I will have a look and see if I can fix it, but for now I've opened the pull request to make other people aware of the bug. If you have any concerns or ideas how to fix it let me know.

Cheers,
Mads