mod_http_oauth2: Switch to '303 See Other' redirects This is the recommendation by draft-ietf-oauth-v2-1-07 section 7.5.2. It is the only redirect code that guarantees the user agent will use a GET request, rather than re-submitting a POST request to the new URL. The latter would be bad for us, as we are encoding auth tokens in the form data.

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.