mod_vcard_muc: Pass room object around instead of JID, hopefully fixing traceback More efficient to pass the object around instead of using the JID and looking up the object when needed. It seems in some (undetermined) cases get_room_from_jid(room.jid) is nil.

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.