lockf is entirely useless and it was a mistake to change to it, go back

to using flock which actually works sensibly. Also always retry the lock
to fix a potential race, and add some extra logging.

server.c

@@ -111,6 +111,7 @@ server_start(int lockfd, char *lockfile)
 	/* The first client is special and gets a socketpair; create it. */
 	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, pair) != 0)
 		fatal("socketpair failed");
+	log_debug("starting server");
 
 	switch (fork()) {
 	case -1: