Stiching together conversation doesn't work properly
GNU social scrambles conversations when stiching them together, e.g.:
This screenshot from quitter.es shows a conversation started on quitter.se. The third notice is actually the conversation starter. The top one is a reply to the third one, but the top one has reply_to=NULL.
My guess is that the starting notice took longer to process, or arrived later. Anyway, if GNU social would store the reply-to-URI for remote notices (even if a notice with that URI doesn't exist on the server (yet)), then the top notice in this case could be updated with the correct local reply-to-ID when the notice with that URI is saved.