Upstream keepalive: clearing of c->data in cached connections. Previously, connections returned from keepalive cache had c->data pointing to the keepalive cache item. While this shouldn't be a problem for correct code, as c->data is not expected to be used before it is set, explicitly clearing it might help to avoid confusion.

# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.


cat << END >> $NGX_AUTO_CONFIG_H

#ifndef $have
#define $have  0
#endif

END