Input filter might free a buffer if there is no data in it, and in case
of first buffer (used for cache header and request header, aka p->buf_to_file)
this resulted in cache corruption.  Buffer memory was reused to read upstream
response before headers were written to disk.

Fix is to avoid moving pointers in ngx_event_pipe_add_free_buf() to a buffer
start if we were asked to free a buffer used by p->buf_to_file.

This fixes occasional cache file corruption, usually resulted
in "cache file ... has md5 collision" alerts.

Reported by Anatoli Marinov.

The ngx_http_keepalive_handler() function is now trying to not
keep c->buffer's memory for idle connections.

This behaviour is consistent with the ngx_http_set_keepalive()
function and it should decrease memory usage in some cases (especially
if epoll/rtsig is used).

*) Log: $apache_bytes_sent removed.  It was renamed to $body_bytes_sent
   in nginx 0.3.10 and the old name is deprecated since then.

*) Variable $bytes_sent.  It replicates variable $bytes_sent as previously
   available in log module only.  Patch by Benjamin Grössing (with minor
   changes).

*) Variables $connection and $connection_requests.  Log module
   counterparts are removed as they aren't used often and there is no
   need to preserve them for efficiency.

SSL: the "ssl_verify_client" directive parameter "optional_no_ca".

This parameter allows to don't require certificate to be signed by
a trusted CA, e.g. if CA certificate isn't known in advance, like in
WebID protocol.

Note that it doesn't add any security unless the certificate is actually
checked to be trusted by some external means (e.g. by a backend).

Patch by Mike Kazantsev, Eric O'Connor.

Limit req: fix of rbtree node insertion on hash collisions.

The rbtree used in ngx_http_limit_req_module has two level of keys, the top is
hash, and the next is the value string itself. However, when inserting a new
node, only hash has been set, while the value string has been left empty.

The bug was introduced in r4419 (1.1.14).
Found by Charles Chen.

Fixed strict aliasing bugs when dealing with IPv4-mapped IPv6
addresses.

The "include" directive should be able to include multiple files if
given a filename mask.  Fixed this to work for "include" directives
inside the "map" or "types" blocks.  The "include" directive inside
the "geo" block is still not fixed.

The bug had appeared in 0.8.43 (r3653).  Patch by Weibin Yao.

Previous code incorrectly used ctx->var_values as an array of pointers to
ngx_http_variable_value_t, but the array contains structures, not pointers.
Additionally, ctx->var_values inspection failed to properly set var on
match.