Elminiate a spurious message when sigchild looses a race to popen(2).

This fixed #143



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@1810 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/mgt_child.c

@@ -305,6 +305,8 @@ mgt_sigchld(struct ev *e, int what)
 	ev_poker = NULL;
 
 	r = wait4(-1, &status, WNOHANG, NULL);
+	if (r == 0)
+		return (0);
 	if (r != child_pid || r == -1) {
 		fprintf(stderr, "Unknown child died pid=%d status=0x%x\n",
 		    r, status);