Changes with nginx 1.5.3 30 Jul 2013

*) Change in internal API: now u->length defaults to -1 if working with
backends in unbuffered mode.

*) Change: now after receiving an incomplete response from a backend
server nginx tries to send an available part of the response to a
client, and then closes client connection.

*) Bugfix: a segmentation fault might occur in a worker process if the
ngx_http_spdy_module was used with the "client_body_in_file_only"
directive.

*) Bugfix: the "so_keepalive" parameter of the "listen" directive might
be handled incorrectly on DragonFlyBSD.
Thanks to Sepherosa Ziehau.

*) Bugfix: in the ngx_http_xslt_filter_module.

*) Bugfix: in the ngx_http_sub_filter_module.