[multi-sources] closes #1918120: drop behaviour leading to wrong result as demonstrated by the ticket The formerly implemented behaviour doesn't seems to be useful, nor to have a chance to be correct. At least no test case demonstrate the opposite, so I've dropped it.

[session] enforce coherency of login/passwd couple values when no anonymous user (closes: #1910849) None may be returned for both if anonymous connection is not allowed or if an empty login is used in configuration Raise ConfigurationError is anonymous login is non-ascii (convention)

[session] take care of non-ascii characters in login and session id (closes: #1910849) We ensure a valid <str> conversion of the session id by using unormalize() at initialization.