Redesign of request cleanup:

  - A new End-Of-Request bucket is pushed through the output filter
    chain after the last bucket of the response.
  - This bucket gets destroyed by ap_core_output_filter() after the
    buckets in front of it have been sent.
  - The destroy callback of the EOR bucket invokes the access logger
    and frees the request's pool.

With this change, the request logger now runs after the last byte of
the response is _sent_, rather than after the last byte of the response
is _generated_.  This should make the bytes-sent count in the access
log more accurate in cases where the client closes the connection
midway through the sending of the response.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/async-dev@307339 13f79535-47bb-0310-9956-ffa450edef68