Request body: discarded body now treated as no body. Notably, proxying of such requests now uses no Content-Length instead of "Content-Length: 0", and the $content_length variable is empty (instead of "0"). This might be beneficial from correctness point of view, since requests with discarded body, such as during processing of error pages, do not pretend there is a zero-length body, but instead do not contain body at all. For example, this might be important for PUT requests, where a zero-length body could be incorrectly interpreted as a real request body. This also slightly simplifies the code.