Replace tpl_text_event_dup_supersedes() with synthetic message
Replace tpl_text_event_dup_supersedes() with synthetic message

This allows us to handle the case where we get b-supersedes-a, but we've lost
the original message a.

Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets