Fix of "Content-Length" header of MP4 response if start argument was used.

Patch by Piotr Sikora.

Reverted incorrect change in internal md5 (part of r3928).

Fixed compression pointer processing in DNS response greater than 255 bytes.

Thanks to Ben Hawkes.

Fixed utf8 decode (ticket #25).

Patch by Alexey Kuts.

Skipping location rewrite phase for server null location.

Additional headers for proxy/fastcgi/uwsgi/scgi_ignore_headers.

Now the following headers may be ignored as well: X-Accel-Limit-Rate,
X-Accel-Buffering, X-Accel-Charset.

Perl related fixes:

*) Handling of Content-Encoding set from perl.

   This fixes double gzipping in case of gzip filter being enabled while perl
   returns already gzipped response.

*) Fixed macro name.

AIO related fixes:

*) Fix for connection drops with AIO.

   Connections serving content with AIO to fast clients were dropped with
   "client timed out" messages after send_timeout from response start.

*) Fix for socket leak with "aio sendfile" and "limit_rate".

   Second aio post happened when timer set by limit_rate expired while we have
   aio request in flight, resulting in "second aio post" alert and socket leak.

   The patch adds actual protection from aio calls with r->aio already set to
   aio sendfile code in ngx_http_copy_filter().  This should fix other cases
   as well, e.g. when sending buffered to disk upstream replies while still
   talking to upstream.

   The ngx_http_writer() is also fixed to handle the above case (though it's
   mostly optimization now).

Autoindex fixes:

*) Autoindex: escape '?' in file names.

   For files with '?' in their names autoindex generated links with '?' not
   escaped.  This resulted in effectively truncated links as '?' indicates
   query string start.

   This is an updated version of the patch originally posted at [1].  It
   introduces generic NGX_ESCAPE_URI_COMPONENT which escapes everything but
   unreserved characters as per RFC 3986.  This approach also renders unneeded
   special colon processing (as colon is percent-encoded now), it's dropped
   accordingly.

   [1] http://nginx.org/pipermail/nginx-devel/2010-February/000112.html

*) Autoindex: escape html in file names.