* The EUID index is now built, and replication checks are being performed

* The EUID index is now built, and replication checks are being performed
  using it.  It is much faster now because we don't have to scan the entire
  room anymore.  We still need to do two things:
  1. Write a server command to fetch messages by EUID instead of msgnum
  2. Find a way to purge stale EUID index records.