Added find_user and find_group methods. Allow 0* 2* and 3* error codes in try_get_file, not only 0, 200, 201, 202 and 203. This fixed a rather irritating error message in the configuration interface. When a <return code=302> tag has been parsed, all subsequent <insert file=...> would return a parse error. Also removed the configuration interface user database from the list of user databases that is searched by authenticate and authenticate_throw when no user database is specified.