caltechlibrary/dataset: Bug Fix, issue #81

When moving collections between OS/File systems there are case sensisitivity issues that crop up. In particular how Mac OS X currently handles (by default) case assignment in paths versus other OS. When migrating a dataset collection between OS/File system types via zip or tar ball it is a good idea to run `dataset check` and `dataset repair` on the destination system. For pairtree layouts repair will not keep track of the missing JSON records then walk the pair tree and re-attach those it finds fixing the path issue. This is an ugly hack but will keep things workable for now. Long run it might make sense to include an archive verb in the dataset command which ensures portable zip and tar balls since that is easy to support via Go standard packages.dataset is a command line tool, Go package, shared library and Python package for working with JSON objects as collections on disc, in an S3 bucket or in Cloud Storag