Changes with nginx 1.5.10 04 Feb 2014

*) Feature: the ngx_http_spdy_module now uses SPDY 3.1 protocol.
Thanks to Automattic and MaxCDN for sponsoring this work.

*) Feature: the ngx_http_mp4_module now skips tracks too short for a
seek requested.

*) Bugfix: a segmentation fault might occur in a worker process if the
$ssl_session_id variable was used in logs; the bug had appeared in
1.5.9.

*) Bugfix: the $date_local and $date_gmt variables used wrong format
outside of the ngx_http_ssi_filter_module.

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

*) Bugfix: alerts "getsockopt(TCP_FASTOPEN) ... failed" appeared in logs
during binary upgrade on Linux; the bug had appeared in 1.5.8.
Thanks to Piotr Sikora.