Request body: next upstream fix. After introduction of chunked request body handling in 1.3.9 (r4931), r->request_body->bufs buffers have b->start pointing to original buffer start (and b->pos pointing to real data of this particular buffer). While this is ok as per se, it caused bad things (usually original request headers included before the request body) after reinit of the request chain in ngx_http_upstream_reinit() while sending the request to a next upstream server (which used to do b->pos = b->start for each buffer in the request chain). Patch by Piotr Sikora.