Added support for trailers in HTTP responses. Example: ngx_table_elt_t *h; h = ngx_list_push(&r->headers_out.trailers); if (h == NULL) { return NGX_ERROR; } ngx_str_set(&h->key, "Fun"); ngx_str_set(&h->value, "with trailers"); h->hash = ngx_hash_key_lc(h->key.data, h->key.len); The code above adds "Fun: with trailers" trailer to the response. Modules that want to emit trailers must set r->expect_trailers = 1 in header filter, otherwise they might not be emitted for HTTP/1.1 responses that aren't already chunked. This change also adds $sent_trailer_* variables. Signed-off-by: Piotr Sikora <piotrsikora@google.com>