Update message events to include is_mirror_dummy

This can be used by mirroring scripts to only forward messages to users
who do not zulip accounts.

(imported from commit 200d6bcaaf39238bfb01480a9e906d567d4d9e11)

bots/jabber_mirror_backend.py

@@ -236,6 +236,8 @@ class ZulipToJabberBot(object):
         for recipient in msg['display_recipient']:
             if recipient["email"] == self.client.email:
                 continue
+            if not recipient["is_mirror_dummy"]:
+                continue
             recip_email = recipient['email']
             jabber_recipient = zulip_to_jid(recip_email, self.jabber.boundjid.domain)
             outgoing = self.jabber.make_message(