Move old rcube_mail_header class definition to better place

Aleksander Machniak

2012-05-23 43918dd25caac5e3fa6f36516e0a982e0445165d

 program/include/rcube_imap_cache.php

@@ -1146,3 +1146,6 @@
        return $index;
    }
}

// for backward compat.
class rcube_mail_header extends rcube_message_header { }