Use message/external-body MIME type for registering 'redirect' binaries
Refactor fcr:fixity to use ContentExposingResource machinery
Update fcr:fixity to produce asynchronous responses
Check for parent tombstones on 404 errors

Resolves: https://www.pivotaltracker.com/story/show/81855584
Merge pull request #614 from fcrepo4/external-body

Use message/external-body MIME type for registering 'redirect' binaries
Merge pull request #615 from fcrepo4/async-fixity

Async fixity