MEDIUM: proxy: Set http-reuse safe as default.

Change the default for http-reuse from "never" to "safe", as it has been
the recommended setting for a few versions now and backend H2 makes little
sense without it.

Some warnings were removed from the config parser since it can dynamically
be disabled depending on the server's configuration, so there's no need to
disable it on a whole backend just for one server.
2 files changed