mod_http_oauth2: Tweak fallback error text Since the oauth error is more like the error condition, a symbolic error code, not the most human-friendly. Many error cases do have human-readable error descriptions that should be fine on their own, or changed to be. As a fallback, capitalize the error name.

This module helps make BOSH and WebSocket connection endpoints
discoverable via the HTTP method described in
[XEP-0156](https://xmpp.org/extensions/xep-0156.html#http).