merge changes between nginx 1.4.4 and 1.4.5

 Details are as following:

 *) Bugfix: the $ssl_session_id variable contained full session
    serialized instead of just a session id.
    Thanks to Ivan Ristić.

    Changeset: http://hg.nginx.org/nginx/rev/70f4d99ded41

 *) Bugfix: client connections might be immediately closed if deferred
    accept was used; the bug had appeared in 1.3.15.

    Changeset: http://hg.nginx.org/nginx/rev/462ae7eedc68

 *) Bugfix: alerts "zero size buf in output" might appear in logs while
    proxying; the bug had appeared in 1.3.9.

    Changeset:  http://hg.nginx.org/nginx/rev/3b7463b08747

 *) Bugfix: a segmentation fault might occur in a worker process if the
    ngx_http_spdy_module was used.

    Changeset: http://hg.nginx.org/nginx/rev/b8e6297358b5

 *) Bugfix: proxied WebSocket connections might hang right after
    handshake if the select, poll, or /dev/poll methods were used.

    Changeset: http://hg.nginx.org/nginx/rev/560de9681661

    More details are available here:
    http://mailman.nginx.org/pipermail/nginx/2014-January/041839.html

 *) Bugfix: a timeout might occur while reading client request body in an
    SSL connection using chunked transfer encoding.

    Changeset: http://hg.nginx.org/nginx/rev/35b00bcf72fe

    More details are available here:
    http://mailman.nginx.org/pipermail/nginx/2013-November/041178.html

 *) Bugfix: memory leak in nginx/Windows.

    Changeset: http://hg.nginx.org/nginx/rev/fd77e2018652

    Note that this patch is not merged because tengine does not support win32.
trim support variable value (on/off). (https://github.com/alibaba/tengine/issues/368)
Update ngx_http_variables.c
Update ngx_http_variables.c
Merge pull request #408 from lhmwzy/master

在DragonFlyBSD 3.6下编译时发生错误
support for chunked in non-buffer request
Merge pull request #409 from yaoweibin/non_buffer_chunked

support for chunked in non-buffer request
Merge pull request #405 from chobits/nginx-update-1.4.5

merge changes between nginx 1.4.4 and 1.4.5
upgrade bugfix:
http://hg.nginx.org/nginx/rev/7586e7b2dbe9
Merge pull request #410 from cfsego/upgrade

upgrade bugfix: Upstream: ngx_post_event() instead of upgraded call (ticket #503).
Merge pull request #411 from taoyuanyuan/test

It looks good to me.
fixed a variable set but unused warning
Merge pull request #412 from yaoweibin/fixed_warning

fixed a variable set but unused warning