bail out of client_read if we've already decide what to do libevent2 can still somehowe call client_read even in code paths that never enable reading from the evbuffer. Can't reproduce on the libevent in base on OpenBSD. It's a bit ugly, but it's a small workaround for something that otherwise *always* make gmid crash when linked against libevent2. (client_read works under the assumption that c->host != NULL, matched_proxy crashes otherwise.)

add proxying with client certificate test

add a test for the `proxy relay-to' rule

rename `runtime' to `regress' while there also kill an unused rule `regress', it's now redundant since all the tests are run together.