Hacking prosody mod_post_msg to support announcing to MUC

foo.lua

    if message and message.attr.type == "groupchat" then
        local m = hosts[module.host].modules;
        local mu = m.muc;
        local room = mu.rooms[message.attr.to];
        if not room then return 414; end -- better code here. 404?
        message.attr.from = message.attr.to;
        module:log("debug", "Sending %s", tostring(message));
        room:broadcast_message(message);
        return 201;