mod_http_oauth2: Validate consistency of response and grant types Ensure that these correlated fields make sense per RFC 7591 § 2.1, even though we currently only check the response type during authorization. This could probably all be deleted if (when!) we remove the implicit grant, since then these things don't make any sense anymore.

# Introduction

This module sends a [version query][xep0092] to clients when they
connect, and logs the response, allowing statistics of client usage to
be recorded.

Note that since this is per connection, there will be a bias towards
mobile clients on bad connections.

## Example

    info    Running Running Swift version 4.0