Changes with nginx 1.3.15 26 Mar 2013

*) Change: opening and closing a connection without sending any data in
it is no longer logged to access_log with error code 400.

*) Feature: the ngx_http_spdy_module.
Thanks to Automattic for sponsoring this work.

*) Feature: the "limit_req_status" and "limit_conn_status" directives.
Thanks to Nick Marden.

*) Feature: the "image_filter_interlace" directive.
Thanks to Ian Babrou.

*) Feature: $connections_waiting variable in the
ngx_http_stub_status_module.

*) Feature: the mail proxy module now supports IPv6 backends.

*) Bugfix: request body might be transmitted incorrectly when retrying a
request to the next upstream server; the bug had appeared in 1.3.9.
Thanks to Piotr Sikora.

*) Bugfix: in the "client_body_in_file_only" directive; the bug had
appeared in 1.3.9.

*) Bugfix: responses might hang if subrequests were used and a DNS error
happened during subrequest processing.
Thanks to Lanshun Zhou.

*) Bugfix: in backend usage accounting.