mod_http_oauth2: Add Cache-Control and Pragma headers per by RFC 6749 These are mostly for the various Client-facing endpoints, so the chance of browsers being involved is slightly lower than with the User-facing authorization endpoint, which already sent the Cache-Control header. Thanks to OAuch for pointing out.

This module discards typing notifications sent to a bare host JID,
preventing error replies to be sent. These errors are harmless but can
be annoying sometimes if your client shows them prominently.