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.


git-svn-id: svn://svn.nginx.org/nginx/trunk@5104 73f98a42-aea0-e011-b76d-00259023448c
Removed c->single_connection flag.

The c->single_connection was intended to be used as lock mechanism
to serialize modifications of request object from several threads
working with client and upstream connections.  The flag is redundant
since threads in nginx have never been used that way.


git-svn-id: svn://svn.nginx.org/nginx/trunk@5105 73f98a42-aea0-e011-b76d-00259023448c