(#111) - Fixes bugs discovered by couchdb-harness

- #63 (Add the "port" to the Location header)
- #101 (Implement ETag/HEAD, MD5 sums for attachments & revisions for
  documents)
- 'curl friendly' responses (newline after json)
- Removed race conditions for _users/_replicator dbs
- Removes express-added ';charset=utf-8' where relevant
- Rewrite bug fix (doesn't use query params for routing any longer)
- Support 'If-Match' header as a way of supplying a revision. Also
  return an error when multiple conflicting revs are given.
- added a 404 handler for the few rare use cases where the
  'db file not found' error isn't returned.