mod_http_oauth2: Stricten check of urlencoded form data Because type(formdecode("string without equals sign")) == "string", so best avoid continuing in that case, even if strings mostly behave as tables as long as you don't hit one of the __index methods.

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.