"fix" part of test_file for pickling of files; add asserts for mode and tell;
partial add comments (and tests) for different schemes for pickling files


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/pathos/dill@693 8bfda07e-5b16-0410-ab1d-fd04ec2748df
Merge branch 'master' of https://github.com/uqfoundation/dill