gh-517: touch libev event loop after fork for proper reinit

src/main.cc

@@ -363,6 +363,12 @@ background()
 	if (setsid() == -1)
 		goto error;
 
+	/*
+	 * tell libev we've just forked, this is necessary to re-initialize
+	 * kqueue on FreeBSD.
+	 */
+	ev_loop_fork(cord()->loop);
+
 	/*
 	 * reinit signals after fork, because fork() implicitly calls
 	 * signal_reset() via pthread_atfork() hook installed by signal_init().