bugfix: nginx did not destroy the cycle memory pool before the daemon process exits.

This is to make the nginx ASAN or Valgrind clean in daemon mode. It is
also meaningful when we have more sophisticated cleanup work needed in
the configuration initialization phase and handlers like init_by_lua*.

patches/nginx-1.13.6-daemon-destroy-pool.patch

@@ -0,0 +1,12 @@
+diff --git a/src/os/unix/ngx_daemon.c b/src/os/unix/ngx_daemon.c
+index ab672110..f259af31 100644
+--- a/src/os/unix/ngx_daemon.c
++++ b/src/os/unix/ngx_daemon.c
+@@ -23,6 +23,8 @@ ngx_daemon(ngx_log_t *log)
+         break;
+
+     default:
++        /* just to make it ASAN or Valgrind clean */
++        ngx_destroy_pool(ngx_cycle->pool);
+         exit(0);
+     }

util/mirror-tarballs

@@ -65,6 +65,10 @@ if [ "$answer" = "Y" ]; then
     echo "$info_txt applying the resolver_conf_parsing patch for nginx"
     patch -p1 < $root/patches/nginx-$main_ver-resolver_conf_parsing.patch || exit 1
     echo
+
+    echo "$info_txt applying the daemon-destroy-pool patch for nginx"
+    patch -p1 < $root/patches/nginx-$main_ver-daemon-destroy-pool.patch || exit 1
+    echo
 fi
 
 answer=`$root/util/ver-ge "$main_ver" 1.5.12`