headline message should not have a reply button

[misc@…]

rfc 3921, about xmpp , say, in paragraphe 2.1.1" Types of Message" that message of type headline should not have a reply button :

"No reply to the message is expected, and a compliant client SHOULD present the message in an interface that appropriately differentiates the message from standalone messages, chat sessions, or groupchat sessions (e.g., by not providing the recipient with the ability to reply)."

Currently, there is the same dialog for 'normal' message and for 'headline' message, which is not recommended by the rfc.

[asterix]

this will be done in #1525