Support SIGUSR2 to stop and start logging for an existing server. Also

we currently only have two log levels so just use -v and -vv rather than
-v and -vvvv, and clarify the man page entry for -v.

server.c

@@ -151,7 +151,7 @@ server_start(struct event_base *base, int lockfd, char *lockfile)
 	}
 	close(pair[0]);
 
-	if (log_get_level() > 3)
+	if (log_get_level() > 1)
 		tty_create_log();
 	if (pledge("stdio rpath wpath cpath fattr unix getpw recvfd proc exec "
 	    "tty ps", NULL) != 0)
@@ -365,6 +365,9 @@ server_signal(int sig)
 		}
 		server_add_accept(0);
 		break;
+	case SIGUSR2:
+		proc_toggle_log(server_proc);
+		break;
 	}
 }