Version bump.
Create request object only after the first byte was received.

Previously, we always created an object and logged 400 (Bad Request)
in access log if a client closed connection without sending any data.
Such a connection was counted as "reading".

Since it's common for modern browsers to behave like this, it's no
longer considered an error if a client closes connection without
sending any data, and such a connection will be counted as "waiting".

Now, we do not log 400 (Bad Request) and keep memory footprint as
small as possible.
Use "client_header_timeout" for all requests in a connection.

Previously, only the first request in a connection used timeout
value from the "client_header_timeout" directive while reading
header.  All subsequent requests used "keepalive_timeout" for
that.

It happened because timeout of the read event was set to the
value of "keepalive_timeout" in ngx_http_set_keepalive(), but
was not removed when the next request arrived.
Respect the new behavior of TCP_DEFER_ACCEPT.

In Linux 2.6.32, TCP_DEFER_ACCEPT was changed to accept connections
after the deferring period is finished without any data available.
(Reading from the socket returns EAGAIN in this case.)

Since in nginx TCP_DEFER_ACCEPT is set to "post_accept_timeout", we
do not need to wait longer if deferred accept returns with no data.