merge changes between nginx 1.4.6 and 1.4.7

Details are as following:

* Security: a heap memory buffer overflow might occur in a worker
   process while handling a specially crafted request by
   ngx_http_spdy_module, potentially resulting in arbitrary code
   execution (CVE-2014-0133).
   Thanks to Lucas Molas, researcher at Programa STIC, Fundación Dr.
   Manuel Sadosky, Buenos Aires, Argentina.

   Changeset: http://hg.nginx.org/nginx/rev/e7f7d30196e3

   **Note that this patch is not merged, because this bug has been fixed in Tengine-2.0.2.**

* Bugfix: in the "fastcgi_next_upstream" directive.
   Thanks to Lucas Molas.

   Changeset: http://hg.nginx.org/nginx/rev/b246018860a2