added 'builtin' to getsource to account for calls to getimport for builtins;
better detection of bad repr in getimport -- catch '<>' in dicts, lists, etc;
better resiliance in importable -- if getimport fails getsource and vice versa;
reverted getimportable to point to importable


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/pathos/dill@646 8bfda07e-5b16-0410-ab1d-fd04ec2748df
Merge branch 'master' of https://github.com/uqfoundation/dill