#2819 Managesieve error if plain auth isn't allowed before tls handshake

[Hendrik v. Raven]

If using managesieve with a server allowing plain authentication, but only after tls negotiation (as default in dovecot) squirrelmail fails with the error messages down below. As by the managesieve RFC the server is allowed to change the capabilities after STARTTLS negotiation thus squirrelmail should check for the capailities after the handshake.

[Sun Apr 13 14:52:48 2014] [error] [client ###] PHP Notice: Undefined index: PLAIN in /usr/share/squirrelmail/plugins/avelsieve/include/managesieve.lib.php on line 538, referer: https://###/squirrelmail/src/webmail.php
[Sun Apr 13 14:52:48 2014] [error] [client ###] PHP Notice: Undefined property: DO_Sieve_ManageSieve::$sieve_capabilities in /usr/share/squirrelmail/plugins/avelsieve/include/DO_Sieve_ManageSieve.class.php on line 141, referer: https://###/squirrelmail/src/webmail.php