*) Request body: fixed "501 Not Implemented" error handling.

   It is not about "Method" but a generic message, and is expected to be used
   e.g. if specified Transfer-Encoding is not supported.  Fixed message to
   match RFC 2616.

   Additionally, disable keepalive on such errors as we won't be able to read
   request body correctly if we don't understand Transfer-Encoding used.

*) Request body: $request_body variable generalization.

   The $request_body variable was assuming there can't be more than two
   buffers.  While this is currently true due to request body reading
   implementation details, this is not a good thing to depend on and may
   change in the future.

*) Request body: code duplication reduced, no functional changes.

   The r->request_body_in_file_only with empty body case is now handled in
   ngx_http_write_request_body().

*) Request body: fixed socket leak on errors.

   The r->main->count reference counter was always incremented in
   ngx_http_read_client_request_body(), while it is only needs to be
   incremented on positive returns.

*) Request body: properly handle events while discarding body.

   An attempt to call ngx_handle_read_event() before actually reading
   data from a socket might result in read event being disabled, which is
   wrong.  Catched by body.t test on Solaris.

*) Fixed location of debug message in ngx_shmtx_lock().

*) Core: don't reuse shared memory zone that changed ownership (ticket #210).

   nginx doesn't allow the same shared memory zone to be used for different
   purposes, but failed to check this on reconfiguration.  If a shared memory
   zone was used for another purpose in the new configuration, nginx attempted
   to reuse it and crashed.

*) Core: added debug logging of writev() in ngx_write_chain_to_file().

*) Core: fixed ngx_write_chain_to_file() with IOV_MAX reached.

   Catched by dav_chunked.t on Solaris.  In released versions this might
   potentially result in corruption of complex protocol responses if they
   were written to disk and there were more distinct buffers than IOV_MAX
   in a single write.

Dav: fixed segfault on PUT if body was already read (ticket #238).

If request body reading happens with different options it's possible
that there will be no r->request_body->temp_file available (or even
no r->request_body available if body was discarded).  Return internal
server error in this case instead of committing suicide by dereferencing
a null pointer.

Fixed failure to start cache manager and cache loader processes
if there were more than 512 listening sockets in configuration.

*) Upstream: honor the "down" flag for a single server.

   If an upstream block was defined with the only server marked as
   "down", e.g.

       upstream u {
           server 127.0.0.1:8080 down;
       }

   an attempt was made to contact the server despite the "down" flag.
   It is believed that immediate 502 response is better in such a
   case, and it's also consistent with what is currently done in case
   of multiple servers all marked as "down".

*) Upstream: better detection of connect() failures with kqueue.

   Pending EOF might be reported on both read and write events, whichever
   comes first, so check both of them.

   Patch by Yichun Zhang (agentzh), slightly modified.

Log module counterparts are preserved for efficiency.

Worker processes are now made aware of their sequential number needed
to select CPU affinity mask.  This replaces a workaround from r4865.