code: public ArrayList<User> lookupUsersByEmail (String email)
          throws PersistenceException
      {
          return loadAll(_utable, "where email = " + JDBCUtil.escape(email));
      }
docs: Lookup a user by email address, something that is not efficient and should really only be
  done by site admins attempting to look up a user record.
  
  @return the user with the specified user id or null if no user with that id exists.