added helper methods in 'pointers' for tracking object parents and references;
added 'get_objgraph' for producing visual of reference trail
popuated the registered types dict in 'objects'; made 'succeeds' the default;
fix: pickling for SuperType where instance is not NULL


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/pathos/dill@528 8bfda07e-5b16-0410-ab1d-fd04ec2748df
Merge branch 'master' of https://github.com/uqfoundation/dill