Uncaught exceptions for Digest header on creation

[scossu]

An unsupported digest algorithm on creation raises a ValueError that results in a 500 error. It should produce a 400 error according to https://fcrepo.github.io/fcrepo-specification/#http-post-ldpnr

A malformed digest string containing an = sign results in a 500 error:

  File "lsup/src/lakesuperior/endpoints/ldp.py", line 287, in post_resource
    request.headers['digest'].split('=')
ValueError: too many values to unpack (expected 2)

[scossu]

Fixed in #108.