Merge pull request #17 from BHSPitMonkey/master

Add checks to ensure that extra data files cause validation to fail
no more python2.4 on travis; also tagging v1.0.0!
mknod does not seem to work on os x
documented supported python versions fixes #18
hack to get around multiprocessing bug on travis platform
Update bagit.py

uh-oh tyops :)
Merge pull request #20 from dchud/patch-1

Thanks @dchud