added rmtree and disk_usage functions; python 3.x compatible imports


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/pathos/pox@569 8bfda07e-5b16-0410-ab1d-fd04ec2748df
Merge branch 'master' of https://github.com/uqfoundation/pox