pox.utils.likely_import returns '' for builtins;
klepto.archives._import adjusted accordingly


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/pathos/klepto@590 8bfda07e-5b16-0410-ab1d-fd04ec2748df
Merge branch 'master' of https://github.com/uqfoundation/klepto