mod_http_oauth2: Simplify template using if-falsy operator Relies on Prosody rev af1e3b7d9ea3 which added the {var~if-falsy}, released in 0.12. Since this module requires trunk this is fine.

This module produces more detailed HTTP logs for Prosodys built-in HTTP
server. The format is similar to that of Apache and go into Prosodys
normal logs at the `info` level.