plugin: hidden conversation

[Markus Teich]

Heyho,

I am currently writing a plugin which needs to exchange metadata-messages
between pairs of participants in a chat. I figured out how to hide those
messages so they won't bother the user, but I was not able to find a way to
prevent pidgin from spawning a new tab in the conversation window.

Currently in the "chat-buddy-joined" handler I try to find an existing
conversation with the respective user with
`purple_find_conversation_with_account` and in case there is none yet, I create
it `with purple_conversation_new`. Then I use `purple_conv_im_send_with_flags`
using the PURPLE_MESSAGE_INVISIBLE flag to send the first metadata-message. Can
I prevent popping up a convesation tab/window in the GTK frontend for the sender
AND receiver?

I'm using pidgin v2.11.0.

--Markus