Upgrade from 1.7.11 to 1.7.12.

Temporary disable following third-party modules:
o) arrayvar
o) echo
o) headers_more
o) http_mogilefs
o) drizzle
o) encryptsession
o) forminput
o) iconv
o) let
o) lua
o) memc
o) modsecurity
o) rds_csv
o) rds_json
o) redis2
o) set_misc
o) sflow
o) srcache
o) xrid_header
o) xss

<ChangeLog>

*) Feature: now the "tcp_nodelay" directive works with backend SSL

connections.

*) Feature: now thread pools can be used to read cache file headers.

*) Bugfix: in the "proxy_request_buffering" directive.

*) Bugfix: a segmentation fault might occur in a worker process when

using thread pools on Linux.

*) Bugfix: in error handling when using the "ssl_stapling" directive.

Thanks to Filipe da Silva.

*) Bugfix: in the ngx_http_spdy_module.

</ChangeLog>