mod_authz_delegate: make resistant against startup order issues There is no guarantee that the target_host gets activated and initialized before the host this module is loaded on. As add_default_permission is called during load time by many modules, we need to be prepared to queue stuff.

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.