ffserver: be explicit on failed fork() msg

Signed-off-by: Reynaldo H. Verdejo Pinochet <reynaldo@osg.samsung.com>

ffserver.c

@@ -442,7 +442,7 @@ static void start_children(FFServerStream *feed)
 
         feed->pid = fork();
         if (feed->pid < 0) {
-            http_log("Unable to create children\n");
+            http_log("Unable to create children: %s\n", strerror(errno));
             exit(1);
         }