importable default (source=None) is 'import if not isfrommain';
added isfrommain and isdynamic;


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/pathos/dill@679 8bfda07e-5b16-0410-ab1d-fd04ec2748df
Merge branch 'master' of https://github.com/uqfoundation/dill