phpdoc
Fix XSS on flags label

Signed-off-by: Michael M Slusarz <slusarz@horde.org>
[mms] SECURITY: Fix XSS when flagging a message in dynamic view with a user-defined flag (João Machado <geral@jpaulo.eu>).
Fix double adding of forwarded atachments when clicking on notice to add body text
Don't allow duplicate user-defined flag names